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Class 10 Science Chemistry Chapter 1 MCQ With Answers

Chemistry Class 10 Chapter 1 MCQs On Chemical Reactions and Equations

Chemical Reaction And Equation Class 10 MCQ Question 1.
Which of the following is not a physical change?
(a) Boiling of water to give water vapour.
(b) Melting of ice to give water.
(c) Dissolution of salt in water.
(d) Combustion of Liquefied Petroleum Gas (LPG).
Answer:
(d) Combustion of Liquefied Petroleum Gas (LPG).

Explanation: Since the combustion of Liquefied Petroleum Gas (LPG) produces new substances, a lot of heat is produced along with carbon dioxide and water vapour. It is also irreversible in nature. So it is a chemical change.

However, boiling of water to give water vapour, melting of ice to give water and dissolution of salt in water are physical changes, as here no new substance is formed, only the physical state of the substance changes.

A physical change does not produce a new substance although the initial and final substances appear different and it is reversible.

During a chemical change, the chemical composition of the substance changes and new substances with new properties are formed. Energy is either released or absorbed during a chemical change and it is irreversible.

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Chemical Reactions And Equations Class 10 MCQ Question 2.
Which of the following is (are) an endothermic process(es)?
(I) Dilution of sulphuric acid
(II) Sublimation of dry ice
(III) Condensation of water vapours
(IV) Evaporation of water
(a) (I) and (III)
(b) Only (II)
(c) Only (III)
(d) (II) and (IV)
Answer:

Class 10 Science Chapter 1 MCQ Question 3.
Strong heating of ferrous sulphate leads to the formation of a brown solid and two gases. This reaction can be categorised as:
(a) displacement and redox.
(b) decomposition and redox.
(c) displacement and endothermic.
(d) decomposition and exothermic.
Answer:
(b) decomposition and redox reaction.

Explanation: When FeSO₄ is heated strong, it decomposes to form a brown solid ferric oxide, sulphur dioxide and sulphur trioxide.

In this reaction, FeSO₄ decomposes and forms new products so it is a decomposition reaction. Here FeSO₄ is oxidised to Fe₂O₃ by loss of electrons. So this part of the reaction is oxidation reaction FeSO₄ is also reduced to SO₂ and SO₃ by a gain of electrons.

Hence, the Heating of FeSO₄ is both decomposition and Redox reaction.

Related Theory:
A reaction is called redox when both oxidation and reduction are taking place simultaneously.
The oxidation process involves:

1. Gain of oxygen
2. Loss of hydrogen
3. Loss of electrons

Reduction process involves:

1. Loss of oxygen,
2. Gain of hydrogen
3. Gain of electrons

The substance which loses electrons i.e. gets oxidised, acts as a reducing agent and the substance which gains electrons, i.e. it gets reduced and acts as an oxidising agent.

Alkyne Reactions Cheat Sheet Download.

Class 10 Chemical Reactions And Equations MCQ Question 4.
Which among the following is (are) double displacement reaction(s)?
(I) Pb + CuCl₂ → PbCl₂ + Cu
(II) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
(III) C + O₂ → CO₂
(IV) CH₄ + 2O₂ → CO₂ + 2H₂O
(a) (I) and (IV)
(b) Only (II)
(c) (I) and (II)
(d) (III) and (IV)
Answer:
(b) only (II)
Explanation: A double displacement reaction involves the displacement of two ions of two different compounds that results in the formation of new compounds. Here, only in reaction (II), ions of both reactants are exchanged and two entirely different compounds are formed. For example.
Na₂SO₄ + BaCl₂ → BaSO_4(s) (White ppt) + 2NaCl_(aq)

In a double displacement reaction, exchange of ions takes place i.e., SO₄^2- exchange place with Cl^– ion. It is also called a precipitation reaction as BaSO₄ is precipitated as insoluble salt in the solution.

Ch 1 Science Class 10 MCQ Question 5.
Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of reaction involved?
(I) Displacement reaction
(II) Precipitation reaction
(III) Combination reaction
(IV) Double displacement reaction
(a) Only (I)
(b) Only (II)
(c) Only (IV)
(d) (II) and (IV)
Answer:

Class 10 Chemistry Chapter 1 MCQ Question 6.
When copper turnings are added to silver nitrate solution, a blue coloured solution is formed after some time. It is because copper:
(I) Displaces silver from the solution
(II) forms a blue coloured complex with AgNO₃
(III) Is oxidized to Cu²⁺
(IV) ls reduced to Cu²⁺
(a) (I) and (II)
(b) (II) and (III)
(c) (I) and (III)
(d) (II) and (IV)
Answer:
(c) (I) and (III)
Explanation: Copper is placed above silver in electrochemical series and thus reaction occurs
Cu + 2Ag+ → Cu²⁺ + 2Ag

Chemical Reaction And Equation MCQ Question 7.
One of the following does not happen during a chemical reaction. This is:
(a) Breaking of old bonds and formation of new bonds
(b) Formation of new substances with entirely different properties
(c) Atoms of one element change into those of another element to form new products
(d) A rearrangement of atoms takes place to form new products
Answer:
(c) atoms of one element change into those of another element to form new products. Explanation: It is not atoms but the bonds between these atoms break and form during chemical reactions. Atoms of elements can rearrange but cannot change into other elements.

Chemical Reactions And Equations MCQ Question 8.
You are given the solution of lead nitrate. In order to obtain a yellow precipitate, you should mix with it a solution of:
(a) potassium chloride
(b) potassium nitride
(c) potassium sulphide
(d) potassium iodide
Answer:
(d) potassium iodide

Explanation: Potassium iodide on reacting with lead nitrate gives yellow precipitate of Lead iodide.
2KI + Pb(NO₃)₂ → Pbl₂ + 2KNO₃

MCQ On Chemical Reactions And Equations Question 9.
In which of the following chemical equations do the abbreviations represent the correct states of the reactants and products involved at reaction temperature?
(a) 2H_2(l) + O₂(l) → 2H₂O_(g)
(b) 2H_2(g) + O₂(l) → 2H₂O_(g)
(c) 2H_2(g) + O₂(g) → 2H₂O_(l)
(d) 2H_2(g) + O₂(g) → 2H₂O_(g)
Answer:

Chapter 1 Science Class 10 MCQ Question 10.
Dilute hydrochloric acid is added to granulated zinc taken in a test tube. The following observations are recorded. Point out the correct observation:
(a) The surface of metal becomes shiny.
(b) The reaction mixture turns milky.
(c) Odour of a pungent-smelling gas is recorded.
(d) A colourless and odourless gas is evolved. [Diksha]
Answer:
(d) A colourless and odourless gas is evolved. Explanation: The chemical reaction between dilute hydrochloric acid and granulated zinc is represented as follows:
Zn + 2HCl → ZnCl₂ + H₂↑
The product, zinc chloride, does not turn the reaction milky. Hydrogen gas evolved is colourless and odourless and released by the formation of bubbles. Hence, option (d) is correct.

MCQ Of Chemical Reaction And Equation Question 11.
On heating, a blue coloured powder of copper (II) nitrate in a boiling tube, a black substance X, oxygen gas and a brown gas Y was formed. Select the option which identifies the products correctly:


Answer:
(c) X is Copper Oxide and Y is Nitrogen Dioxide Explanation: When blue coloured powder of copper (II) nitrate is heated, it decomposes to form black coloured substance which is copper oxide, oxygen gas and brown gas nitrogen dioxide.

The chemical equation for the reaction taking place is:

Class 10 Science Ch 1 MCQ Question 12.
In the equation:
Cu + XHNO₃ → CU(NO₃)₂ + yNO₂ + 2H₂O
The values of x and y are:
(a) 3 and 5
(b) 8 and 6
(c) 4 and 2
(c) 7 and 1
Answer:
(c) Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O
Explanation: In order to find the values of x and y, we need to balance the chemical equation by equating the number of atoms of each element on both sides in the given equation.
Cu + XHNO₃ → CU(NO₃)₂ + yNO₂ + 2H₂O

Equating the number of H atoms on both sides as per the law of conservation of mass, x = 4.
Putting this value in either the no. of atoms of N or O,
x = y + 2 means y = x – 2 = 4 – 2 = 2.
Therefore, x = 4 & y = 2 is the correct answer

Chemical equation balance the equation calculator finds the stoichiometric coefficients to balance chemical equations incl.

MCQ Questions For Class 10 Science Chapter 1 Question 13.
In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?
(a) AlCl_3(aq) + 3NH₄OH_(aq) → Al(OH)₃(s) + 3NH₄Cl_(aq)
(b) AlCl_3(aq) + 3NH₄OH_(l) → Al(OH)_3(aq) + 3NH₄Cl_(s)
(c) AlCl_3(aq) + 3NH₄OH_(aq) → Al(OH)_3(s) + 3NH₄Cl_(aq)
(d) AlCl_3(aq) + 3NH₄OH_(aq) → Al(OH)_3(aq) + 3NH₄Cl_(s)
Answer:
(a) AlCl_3(aq) + 3NH4OH_(aq) → Al(OH)3(s) + 3NH4CL_(aq)

Explanation: When ammonium hydroxide solution is added to aluminium chloride solution, a white precipitate of aluminium hydroxide is formed alongwith ammonium chloride solution.

Chemical Equations And Reactions Class 10 MCQ Question 14.
The reaction 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O is an example of:
(I) displacement reaction.
(II) double displacement reaction.
(III) neutralisation reaction.
(IV) combination reaction.
(a) (I) and (II)
(b) (II) and (III)
(c) (III) and (IV)
(d) (I) and (IV)
Answer:

Chemical Equation And Reaction Class 10 MCQ Question 15.
Consider the following chemical equation:
X_(aq) + sodium chloride_(aq) → Y(white ppt) + Sodium nitrate_(aq)

Assertion Reasoning questions Class 10 Science Chapter 1

For the following questions, two statements are given: one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Question 16.
Assertion (A): Following is a balanced chemical equation for the action of steam on iron:
4Fe + 4H₂O_(g) → Fe₃O₄ + 4H₂
Reason (R): The law of conservation of mass holds good for a chemical equation.
Answer:
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).

Explanation: Iron (Fe) metal does not react with cold or hot water but it reacts with steam to form a metal oxide and hydrogen.

The law of conservation of mass holds good for a chemical reaction. The statement is true but it does not explain the equation given in the Assertion.

Question 17.
Assertion (A): Magnesium ribbon burns with a dazzling white flame.
Reason (R): Magnesium ribbon undergoes physical change on burning and melts.
Answer:

Question 18.
Assertion (A): While equalizing the number of atoms to balance a chemical equation, we alter the formula of the compounds or elements involved in the reaction.
Reason (R): Chemical equation is balanced by making the number of atoms of each element equal on both sides of the arrow.
Answer:
(d) (A) is false, but (R) is true.
Explanation: A chemical equation is balanced by making the number of atoms of each element equal on both sides of the arrow without altering the formula of the compounds or elements involved in the reaction. It is balanced by putting coefficients in front of the compounds or elements.

Question 19.
Assertion (A): The reaction of calcium oxide with water to produce slaked lime releasing a large amount of heat is a combination reaction.
Reason (R): Double displacement reactions are the reactions in which there is an exchange of ions between the reactants.
Answer:
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).

Explanation: The reaction of calcium oxide with water to produce sLaked lime releasing a large amount of heat is a combination reaction as the two reactants combine to form a single product.

Whereas, in a double displacement reaction, there will be two reactants and two products which are formed by the exchange of ions between the reactants.

Question 20.
Assertion (A): The decomposition reaction of silver chloride into silver and chlorine is an exothermic process.
Reason (R): Reactions in which energy is absorbed are known as endothermic reactions.
Answer:

Question 21.
Assertion (A): Zinc and lead displace copper from their compounds.
Reason (R): Zinc and lead are more reactive than copper.
Answer:

Competency-Based Questions (CBQs)

Question 1.

During a chemical reaction atoms of one element do not change into those of another element. Nor do atoms disappear from the mixture or appear from elsewhere. Actually, chemical reactions involve the breaking and making of bonds between atoms to produce new substances.

To demonstrate a reaction, 2 g of silver chloride is taken in a china dish and placed in sunlight.
(A) What will you observe after some time?
(B) What is this reaction known as?
(C) Write the balanced chemical equation for this reaction.
(D) Give reasons for the observations.
Answer:

Question 2.
Whitewash is a very low-cost type of paint made from slaked lime (calcium hydroxide) and chalk (whiting). Chalk is calcium carbonate. Slaked lime turns into chalk by reacting with carbon dioxide in the air over several days. This causes crystallization, which binds and strengthens the coating. Various other additives can be used.

Solid calcium oxide reacts vigorously with water to form calcium hydroxide, accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form a solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
(I) It is an endothermic reaction.
(II) It is an exothermic reaction.
(III) The pH of the resulting solution will be more than seven.
(IV) The pH of the resulting solution will be less than seven.
(a) (I) and (II)
(b) (II) and (III)
(c) (I) and (IV)
(d) (III) and (IV)
Answer:
(b) (II) and (III)

Explanation: Slaking of lime is an exothermic reaction because a large amount of heat is produced during the reaction. The heat can be felt by touching the beaker from the outside. The resulting compound Ca(OH)2, which is also called slaked lime, turns red litmus solution to blue and hence, proves it to be a basic solution. Thus, the pH of this solution will be more than seven.

Question 3.
Shalini was quite interested in observing the changes that take place during chemical reactions but was always afraid of entering the chemistry lab. When she spoke to her chemistry teacher regarding this, the teacher suggested that she should perform a simple experiment under her guidance to overcome her fear and at the same time she could observe the changes that take place during a chemical reaction.

She took about 2 g of ferrous sulphate crystals in a dry boiling tube and heated it over the
flame of a burner. She noticed change of colour of the ferrous sulphate crystals and could also smell the characteristic odour of burning sulphur.
(A) What change in colour did Shalini observe?
Answer:
Shalini observed that the green colour of ferrous sulphate crystals changed to white as it loses water when heated.
FeSO₄.7H₂O → FeSO₄ + 7H₂O

(B) Why did Shalini get the characteristic odour of burning sulphur?
Answer:

(C) What type of reaction takes place when ferrous sulphate is heated?
Answer:
The type of reaction taking place is the thermal decomposition reaction. The chemical equation for the reaction taking place is:

(D) Give another example of such type of reactions.
Answer:

Question 4.
The production of hydrogen from water via electrolysis is a clean process, resulting in only oxygen being produced as a by-product. If the electricity required to split the water into hydrogen and oxygen is supplied via a renewable energy source then the process is environmentally benign.The water electrolysis hydrogen (oxygen) plant is equipment that electrolyzes water to produce hydrogen and oxygen by using lye as an electrolyte.

Electrolysis of water is a decomposition reaction. The mole ratio of hydrogenand oxygen gases liberated during the electrolysis of water is:
(a) 1:1
(b) 2:1
(c) 4:1
(d) 1:2
Answer:
(b) 2:1

Explanation: The balanced chemical equation for the electrolysis of water is:

The mole ratio of hydrogen and oxygen gases Liberated during electrolysis of water is 2:1 by volume.

In a decomposition reaction, a compound is broken down into its simpler forms. During electrolysis, water is broken down into oxygen gas and hydrogen gas due to the passage of electric current through it.

Question 5.
Redox reactions are an important class of reactions. The oxidation and reduction reactions always occur simultaneously, such class of chemical reactions is named as the redox reaction or Oxidation-Reduction reaction.

The substance getting reduced in a chemical reaction is known as the oxidizing agent, while a substance that is getting oxidized is known as the reducing agent. The activity in which copper powder is taken in a china dish and heated helps in understanding redox reactions.
(A) What happens when copper powder is heated in a china dish? Explain your observation.
Answer:
When copper powder is heated in a china dish, the surface of copper powder is coated with black copper oxide as oxidation of copper takes place by addition of oxygen to copper.
2Cu + O₂ → 2CuO

(B) What will you observe if hydrogen gas is passed over the heated material obtained in (A) above?
Answer:
When hydrogen gas is passed over heated material CuO, the black coating on the surface turns brown as the reverse reaction takes place and copper is formed.
CuO + H₂ → Cu + H₂O

(C) Identify the substance oxidized and substance reduced in the reaction at (B) above.
Answer:

(D) Identify the correct statement:
In the reaction between lead sulphide and hydrogen peroxide shown by the equation below,
PbS + 2H₂O₂ → PbSO₄ + 4H₂O,
(a) Lead sulphide Is reduced and Hydrogen peroxide is oxidized.
(b) Lead sulphide is oxidized and Hydrogen peroxide is reduced.
(c) Lead sulphate is oxidized and water is reduced.
(d) Lead sulphate is reduced and water is oxidized.
Answer:

Question 6.
Rancidification is the process of complete or incomplete oxidation or hydrolysis of fats and oils when exposed to air, light, or moisture or by bacterial action, resulting in unpleasant taste and odor. Specifically, it is the hydrolysis or autoxidation of fats into short-chain aldehydes and ketones, which are objectionable in taste and odor. When these processes occur in food, undesirable odors and flavors can result.

Which of the following gases can be used for the storage of fresh sample of an oil for a long time?
(a) Carbon dioxide or oxygen
(b) Nitrogen or oxygen
(c) Carbon dioxide or helium
(d) Helium or nitrogen
Answer:
(d) Helium or nitrogen

Explanation: Inert gases like helium or nitrogen both can be used for the storage of fresh sample of oil for a Long time, as they do not react with most elements, including oxygen. Thus these gases create an inert environment for the oil and prevent its reaction (oxidation) with any element in the environment. Hence, stopping it from becoming rancid.

Question 7.
A student takes two test tubes. In the first test tube, he takes lead nitrate solution and in the second he takes a few zinc granules. He adds potassium iodide solution to lead nitrate solution in the first test tube. He adds dilute sulphuric acid in the second test tube containing zinc granules.
(A) What is observed in the first test tube on adding potassium iodide solution?

Answer:
(c) Both (II) and (III)

Explanation: When potassium iodide solution is added to lead nitrate solution in a test tube, a yellow precipitate of Lead iodide is formed. The equation of the reaction taking place is:

Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)

(B) Select the correct observations:
When dilute sulphuric acid is added to a few zinc granules in the second test tube,
(I) Bubbles of hydrogen gas can be seen around the zinc granules.
(II) Bubbles of carbon dioxide can be seen around zinc granules.
(III) The flask becomes hot
(IV) Colour of solution changes to blue,
(a) Only (I)
(b) Both (I) and (III)
(c) Both (II) and (III)
(d) (I), (III) and (IV)
Answer:
(b) Both (I) and (III)

Explanation: When diluting sulphuric acid is added to zinc granules in a conical flask, the equation of the reaction taking place is:
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq)+ H₂(g)

(C) Select the incorrect statement(s):
(I) Both the reactions are accompanied by a change in colour.
(II) A precipitate is formed in the first test tube only.
(III) Gas is evolved in the second test tube only.
(IV) Both the reactions are examples of double displacement reactions.
(a) Both (I) and (III)
(b) Both (I) and (IV)
(c) Both (II) and (III)
(d) Both (I) and (II)
Answer:

(D) Suppose we add dil hydrochloric acid in place of sulphuric acid in the second test tube. Select the correct observation:
(a) Chlorine gas will be evolved.
(b) The test tube will become cold as heat is absorbed during this reaction.
(c) Hydrogen gas will be evolved.
(d) A precipitate of zinc chloride will be formed
Answer:

(E) The type of reaction taking place when water is added slowly to a small amount of calcium oxide in a beaker is:
(I) Combination Reaction
(II) Displacement reaction
(III) Exothermic reaction
(IV) Endothermic reaction
(a) Both (I) and (III)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (II) and (IV)
Answer:

Question 8.
You must have seen that your mother stores fried food items such as boondi raita, chips, mixture, banana chips and other such items properly. This is because their smell and taste change due to the oxidation of fried food items and food becomes unfit for human consumption.

Why are anti-oxidants added to fat and oil-containing food items?
Answer:
Anti-oxidants are added to fat and oil-containing food items to prevent their oxidation which is known as rancidity which makes food smell bad and changes its taste.

Question 9.
Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Chemical reactions must be distinguished from physical changes. Physical changes include changes of state, such as ice melting to water and water evaporating to vapour. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same. However, if water, as ice, liquid, or vapour, encounters sodium metal (Na), the atoms will be redistributed to give the new substances molecular hydrogen (H₂) and sodium hydroxide (NaOH). By this, we know that a chemical change or reaction has occurred.
(A) Which of the following are physical changes?
(I) Melting of wax
(II) Burning of wax
(III) Rusting of iron
(IV) Evaporation of water
(a) Both (I) and (III)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (II) and (IV)
Answer:
(c) Both (I) and (IV)

Explanation: Melting of wax and evaporation of water are physical change as they undergo only change in their physical states without any change in their chemical composition. Whereas, burning of wax is a chemical change as carbon dioxide and water are formed when wax is burned. Rusting of iron is also a chemical change as iron undergoes oxidation in the presence of moisture to form rust or iron oxide.

(B) A chemical reaction does not involve:
(a) Formation of new substances having entirely different properties than that of the reactants
(b) Breaking of old chemical bonds and formation of new chemical bonds
(c) Rearrangement of the atoms of reactants to form new products
(d) Changing of the atoms of one element into those of another element to form new products
Answer:

(C) Quick lime is used in whitewashing because
(a) It is cheap
(b) It forms limestone with water which has a nice color.
(c) It forms slaked lime with water which reacts with atmospheric carbon dioxide to form limestone.
(d) It is easy to use
Answer:

(D) Which of the following are endothermic processes?
(I) Burning of natural gas
(II) Dilution of an acid
(III) Evaporation of water
(IV) Sublimation of camphor (crystals)
(a) (I) and (II)
(b) (II) and (III)
(c) (IV) and (IV)
(d) (III) and (IV)
Answer:

(E) The following reaction is used for the preparation of oxygen gas in the laboratory

Which of the following statement about the reaction is correct?
(a) It is a displacement reaction and endothermic in nature.
(b) it is a decomposition reaction and exothermic in nature.
(c) It is a decomposition reaction and endothermic in nature.
(d) It is a photochemical decomposition reaction and exothermic in nature.
Answer:
((c) It is a decomposition reaction and endothermic in nature.

Explanation: It is a decomposition reaction as a single reactant splits up into two products, namely, KCl and O₂, by absorbing energy in the form of heat.

It is an endothermic reaction as heat is absorbed in this reaction.

Question 10.
Many materials over time can be prone to corrosion and wear Iron is one such metal. Having a protective later and proper preparation can certainly help materials last longer and have other properties integrated into it.

A substance X used for coating iron articles is added to a blue solution of a reddish-brown metal Y. the colour of the solution gets discharged. Identify X and Y and also the type of reaction.
Answer:
We are given that the metal Y is reddish brown in colour. This metal is copper and the blue solution of Y is copper sulphate. Also, zinc is used in protecting iron articles and this process is called galvanisation. As Zinc is more reactive than copper it displaces copper from its salt solution, copper sulphate.
Zn + CUSO₄ → ZnSCO₄ + Cu
So, X is zinc, while Y is copper.

Question 11.
Double displacement reactions may be defined as the chemical reactions in which one component each of both the reacting molecules is exchanged to form the products. During this reaction, the cations and anions of two different compounds switch places, forming two entirely different compounds.

Double displacement reactions generally take place in aqueous solutions in which the ions precipitate and there is an exchange of ions.

Double displacement reactions can be further classified as neutralization and precipitation reactions.
(A) What is the precipitate formed on mixing the solution of barium chloride and sodium sulphate?
(a) Barium sulphate
(b) Sodium chloride
(c) Barium sulphite
(d) Sodium sulphite
Answer:
(a) Barium Sulphate

Explanation: When a solution of barium chloride is mixed with a solution of sodium sulphate, a precipitate of barium sulphate is formed along with sodium chloride.
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + NaCl(aq)

(B) When Potassium iodide solution is added to lead(II) nitrate solution,
(I) lead (II) iodide precipitates out of the solution as a yellow solid
(II) Potassium nitrate precipitates out of the solution as a yellow solid
(III) Potassium displaces lead from lead nitrate solution.
(IV) Exchange of lead and potassium ions takes place
(a) Both (I) and (III)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (II) and (IV)
Answer:

(C) Identify the precipitate obtained by the reaction between lead nitrate and sodium sulphate.
(a) PbS
(b) Pb(SO₄)₂
(c) PbSO₄
(d) NaNO₂
Answer:
(c) PbSO₄
Explanation: Lead nitrate reacts with sodium sulphate solution to form a precipitate of lead sulphate and sodium nitrate.
Pb(NO₃)₂(aq)+ Na₂SO₄(aq) → PbSO₄(s) + 2NaNO₃(aq)

This is a double displacement reaction as the exchange of lead and sodium ions is taking place.

(D) Which one of the following is true about a double displacement reaction?
(I) Electrolysis of water is an example of this reaction.
(II) Two compounds exchange ions to form new compounds.
(III) Only a single product is formed.
(IV) Reaction between magnesium oxide and dilute hydrochloric acid is an example for this reaction.
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) Both (II) and (III)
(d) Both (II) and (IV)
Answer:

(E) Identify the incorrect statement regarding double displacement reactions:
(a) All double displacement reactions are precipitation reactions.
(b) All neutralization reactions between acids and bases are double displacement reactions
(c) The reaction between vinegar and baking soda is an example of a double displacement reaction.
(d) Reaction between silver nitrate solution and sodium chloride solution is an example of a double displacement reaction.
Answer:

Question 12.
Thermite is a pyrotechnic composition of metal powder fuel and metal oxide. When ignited by heat, thermite undergoes an exothermic oxidation-reduction reaction. Most varieties are not explosive but can create brief bursts of high temperature in a small area. Its form of action is similar to that of other fuel-oxidizer mixtures, such as black powder. Thermites have diverse compositions. Fuels include aluminium, magnesium, titanium, zinc, silicon, and boron. Aluminium is common because of its high boiling point. Oxidizers include boron(III) oxide, silicon(IV) oxide, chromium(III) oxide, manganese(IV) oxide, iron(III) oxide, iron(II, III) oxide, copper(II) oxide, and lead(ll,IV) oxide.

In this reaction mention the substance getting oxidized and the substance getting reduced.
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe
Answer:
Oil and fat containing food items are flushed with nitrogen while packing them as nitrogen is an inert gas and prevents fried food materials from getting rancid.

Question 13.
A synthesis or combination reaction is a reaction in which simple compounds combine to make a more complex one. The opposite of a combination reaction is a decomposition reaction in which a single substance splits into two or more substances. We also have a single displacement reaction (in which a more reactive element displaces a less reactive element from its compound) and a double displacement reaction (in which the exchange of ions takes place between two compounds). Having a thorough understanding of the types of reactions will be useful for predicting the products of an unknown reaction.
(A) A student performed several experiments and then noted down his observations in a tabular form as given below:

Select the option that correctly describes the conclusions made by the student regarding type of reaction taking place:
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) Both (II) and (III)
(d) (I), (III) and (IV)
Answer:
(d) Both (III) and (IV)

Explanation : When barium chloride solution is added to copper sulphate soLution, a white precipitate of barium sulphate is formed alongwith copper chloride solution.

This is an example of precipitation reaction as a precipitate of barium sulphate is formed. It is also a double displacement reaction as the Ba²⁺ and Cu²⁺ ions form new compounds by exchanging their ions. The equation of the reaction talcing place is:
BaCl₂(aq) + CuSO₄(aq) → BaSO₄(s) + CuCl₂(aq)

(B) When a metal X, which is used for coating iron articles, is added to a blue solution of a reddish brown metal Y, the color of the solution gets discharged.
Select the option which correctly identifies the metals X and Y and the type of reaction taking place.

Answer:

(C) The type of reaction taking place when barium chloride solution is added to copper sulphate solution is:
(I) Combination reaction
(II) Displacement reaction
(III) Double Displacement reaction
(IV) Precipitation reaction
(a) Only (I)
(b) Only (II)
(c) Both (II) and (IV)
(d) Both (III) and (IV)
Answer:

(D) Identify the incorrect statement:
(a) Burning of natural gas is a decomposition reaction.
(b) Burning of hydrogen gas in air is a combination reaction
(c) Reaction between most metals and dilute hydrochloric acid is a displacement reaction.
(d) Reaction between an acid and a base is an example of double displacement reaction.
Answer:

(E) Which of the following statement(s) are correct?
(I) The precipitation reactions produce insoluble salts.
(II) Neutralization reactions are single displacement reactions.
(III) Decomposition reactions can be carried out only in presence of heat or light.
(IV) Displacement reactions are opposite of combination reactions.
(a) Only (I)
(b) Only (II)
(c) Both (I) and (III)
(d) Both (II) and (IV)
Answer:
(a) Only (I)

Explanation: Precipitation reactions are the reactions in which an insoluble substance or precipitate is formed. Neutralization reactions are the reactions between an acid and a base and are double displacement reactions. Decomposition reactions require energy in the form of heat, light or electricity. Decomposition reactions are the opposite of combination reactions.

Very Short Answer Type Questions

Question 1.
What happens when sodium sulphate solution is added to barium chloride solution?
Answer:
When sodium sulphate solution is added to barium chloride solution, a white precipitate of barium sulphate is formed.
The equation of the reaction taking place is:
Na₂SO₄((aq) + BaCl₂(aq) →BaSO₄(s) + 2NaCl(aq)

Question 2.
An aqueous solution of metal nitrate P reacts with sodium bromide solution to form yellow ppt of compound Q which is used in photography. Q on exposure to sunlight undergoes decomposition reaction to form metal present in P along with reddish-brown gas. Identify P & Q.
Answer:
As the compound Q is formed by the reaction between P (metal nitrate solution) and sodium bromide solution, Q is silver bromide which is used in photography.

Further, Q undergoes decomposition in the presence of sunlight to form silver and bromine gas. As silver is formed above, the metal nitrate is silver nitrate.

P – silver nitrate (AgNO₃)
Q – silver bromide (AgBr).

Question 3.
What can be seen when a strip of copper metal is placed in a solution of silver nitrate?
Answer:
When a strip of copper metals is placed in a solution of silver nitrate, copper displaces silver from silver nitrate solution as copper is a more reactive metal than silver. Copper nitrate is formed with a shiny greyish-white deposit of silver on the copper strip.
2AgNO₃ + Cu → Cu(NCO₃)₂ + 2Ag

Question 4.
Name and state the law which is kept in mind when we balance chemical equations.
Answer:
The law which is kept in mind when we balance chemical equations is the law of conservation of mass which states that “Matter can neither be created nor be destroyed”. It means that the total mass of atoms of reactants = the total mass of atoms of products, as atoms can neither be created nor be destroyed.

Question 5.
Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water, a compound made up of hydrogen and oxygen is used to extinguish fire. Why?
Answer:
The compound made up of hydrogen and oxygen is water (H20) which has properties that are different from properties of H₂ and O₂ as it is formed by the chemical reaction between hydrogen and oxygen gases. While hydrogen and oxygen are gases at room temperature, water is a liquid at room temperature.

Question 6.
If copper metal is heated over a flame, it develops a coating. What is the colour and composition of the coating?
Answer:

Question 7.
Write a balanced chemical equation to represent the following reaction: carbon monoxide reacts with hydrogen gas at 340 atm to form methyl alcohol.
Answer:

Question 8.
Write a balanced chemical equation for the reaction between sodium chloride and silver nitrate indicating the physical state of the reactants and the products.
Answer:
When silver nitrate solution is added to sodium chloride solution, a white precipitate of silver chloride is formed along with sodium nitrate solution.
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Question 9.
Complete and balance the following:
Fe₂O₃ + Al →
Answer:

MCQ Questions for Class 10 Science with Answers

Class 10 Science Chemistry MCQ:

• Chemical Reactions and Equations Class 10 MCQ
• Acids, Bases and Salts Class 10 MCQ
• Metals and Non-metals Class 10 MCQ
• Carbon and Its Compounds Class 10 MCQ
• Periodic Classification of Elements Class 10 MCQ

Class 10 Science Chemistry Chapter 2 MCQ With Answers

Chemistry Class 10 Chapter 2 MCQs On Acids, Bases and Salts

Acid Bases And Salts Class 10 MCQ Question 1.
What happens when the solution of an acid is mixed with the solution of a base in a test tube?
(I) The temperature of the solution increases
(II) The temperature of the solution decreases
(III) The temperature of the solution remains the same
(IV) Salt formation takes place
(a) Only (I)
(b) (I) and (III)
(c) (I) and (III)
(d) (I) and (IV)
Answer:
(d) (I) and (IV)

Explanation: When an acid reacts with a base, a neutral salt is formed by the neutralisation process. As the neutralisation process is an exothermic reaction, the temperature of the solution increases.
Acid + Base → Salt + Water

Acids Bases And Salts Class 10 MCQ Question 2.
If 10 mL of H₂SO₄ is mixed with 10 mL of Mg(OH)₂ of the same concentration, the resultant solution will give the following colour with a universal indicator:
(a) Red
(b) Yellow
(c) Green
(d) Blue
Answer:
(c) Green.
Explanation: If 10 mL of H₂SO₄ is mixed with 10 mL of Mg(OH)₂ of the same concentration, the resultant solution be MgS04 which is a neutral salt and universal indicator will give the green colour in this solution:

Related Theory:
When an acid reacts with a base it forms salt and water. As a result, acidic properties disappear The process is called neutralisation. For a neutral solution. pH is 7. The solution having pH 7 wilL turn green in colour in universal indicator.

This online pH calculator is designed to determine the pH of an aqueous solution of a given chemical compound.

Class 10 Science Chapter 2 MCQ Question 3.
Which of the following saLts does not contain water of crystatUsatlon?
(a) Blue vitriol
(b) Baking soda
(c) Washing soda
(d) Gypsum
Answer:

Acid Base And Salts Class 10 MCQ Question 4.
A visually challenged student has to perform a lab test to detect the presence of acid in a given solution. The acid-base indicator preferred by him will be:
(a) Blue litmus
(b) Clove oil
(c) Red cabbage extract
(d) Hibiscus extract
Answer:
(b) Clove oil

Explanation: Clove oil is an olfactory indicator. These are the substances that give one type of odour in an acidic medium so a visually challenged student prefers to use clove oil as an acid-base indicator.

As in basic solutions, the smell of clove oil disappears while the smell is retained when mixed with an acid, on the other hand, blue litmus, red cabbage extract and hibiscus extract wouLd not be used as acid-base indicators because in these indicators there will be a change in the colour.

Class 10 Acids Bases And Salts MCQ Question 5.
Baking soda is a mixture of:
(a) Sodium carbonate and acetic acid
(b) Sodium carbonate and tartaric acid
(c) Sodium hydrogen carbonate and tartaric acid
(d) Sodium hydrogen carbonate and acetic acid
Answer:

MCQ Of Acid Base And Salts Class 10 Question 6.
Which of the following gives the correct increasing order of acid strength?
(a) Water < acetic acid < hydrochloric acid
(b) Water < hydrochloric acid < acetic acid
(c) Acetic acid < water < hydrochloric acid
(d) Hydrochloric acid < water < acetic acid
Answer:

Ch 2 Science Class 10 MCQ Question 7.
What is observed when we pour a drop of acetic acid first on red and then on blue litmus papers?
(a) Red litmus paper becomes colourless and blue litmus paper remains blue.
(b) Red litmus paper turns blue and blue litmus paper remains blue.
(c) Red litmus paper remains red and blue litmus paper turns red.
(d) Red litmus paper turns blue and blue litmus paper turns red.
Answer:

Class 10 Science Ch 2 MCQ Question 8.
Sodium hydrogen carbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved?
(I) It turns lime water milky.
(II) It extinguishes a burning splinter.
(III) It dissolves in a solution of sodium hydroxide.
(IV) It has a pungent odour.
(a) (I) and (II)
(b) (I), (II) and (III)
(c) (II), (III) and (IV)
(d) (I) and (IV)
Answer:
(b) (I), (II) and (III)

Explanation: Reaction of sodium hydrogen carbonate with acetic acid forms sodium acetate and water with carbon dioxide (CO₂) gas.

CO₂ does not have a pungent smell but it shows all the other three properties:

1. turns lime water milky,
2. is a non-supporter of combustion and
3. absorbed by strong alkalis such as NaOH.

MCQ Questions For Class 10 Science Chemistry Chapter 2 Question 9.
Common salt besides being used in the kitchen can also be used as the raw material for making:
(I) Washing soda
(II) Bleaching powder
(III) Baking soda
(IV)Slaked Urne
(a) (I) and (II)
(b) (I), (II) and (IV)
(c) (I) and (III)
(d) (I), (III) and (IV)
Answer:

Acids Bases And Salts MCQ Question 10.
To protect against tooth decay we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is:
(a) Acidic
(b) Neutral
(c) Basic
(d) Corrosive
Answer:
(c) Basic

Explanation: The toothpaste commonly used is alkaline or basic in nature as they contain mild bases such as sodium fluoride or sodium bicarbonate in their composition.

The base reacts with the acid formed during bacterial action in the mouth and neutralises its bad effects. Thus, preventing tooth decay. So, they can neutralize the effect of extra acids being formed in the mouth cavity which are mainly responsible for tooth decay.

Related Theory
When we eat sweet things, the pH of our mouth falls below 5.5 (moderately acidic) as the oral bacteria release acid while acting on sugars present in our food. The acidic conditions are capable of corroding the enamel which is made up of calcium phosphate. This causes the tooth to decay.

MCQ Questions For Class 10 Science Chapter 2 Question 11.
Match the chemical substances given in Column I with their appropriate application given in Column II:

Answer:

Chapter 2 Science Class 10 MCQ Question 12.
Which of the following phenomena occur, when a small amount of acid is added to water?
(I) Ionisation
(II) Neutralisation
(III) Dilution
(IV)Salt formation
(a) (I) and (II)
(c) (II) and (III)
(b) (I) and (III)
(d) (II) and (IV)
Answer:

Class 10 Chemistry Chapter 2 MCQ Question 10.
To protect against tooth decay we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is:
(a) Acidic
(b) Neutral
(c) Basic
(d) Corrosive
Answer:
(c) Basic

Explanation: The toothpaste commonly used is alkaline or basic in nature as they contain

Class 10 Acid Base And Salt MCQ Question 13.
A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish-blue:
(a) Lemon juice
(b) Vinegar
(c) Common salt
(d) An antacid
Answer:
(d) An antacid

Explanation: pH paper gives greenish-blue colour in a weak alkaline medium so antacid [Mg(OH)₂] which is an alkaline compound will show greenish-blue color on pH paper.

Related Theory
Lemon fruit contains citric acid, vinegar has acetic acid and common salt is the neutral salt the clear super natant solution turns the pH paper yellowish-orange means the given sample of soil is acidic so it can be neutralised by base/alkaline solution.

MCQ On Acids Bases And Salts Class 10 Question 14.
Which of the following is not a mineral acid?
(a) Hydrochloric acid
(b) Citric acid
(c) Sulphuric acid
(d) Nitric acid
Answer:

Class 10 Chapter 2 Science MCQ Question 15.
Which of the following is/are true when HCl_(g) is passed through water?
(I) It does not ionise in the solution as it is a covalent compound.
(II) It ionises in the solution.
(III) It gives both hydrogen and hydroxyl ions in the solution.
(IV) It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule.
(a) Only (I)
(b) Only (III)
(c) (II) and (IV)
(d) (III) and (IV)
Answer:
(c) (II) and (IV)

Explanation: HCl, is a polar covalent compound, easily ionises in water to form hydronium (H₃O⁺) and chloride ions (Cl^–). HCl (a strong acid) ionises completely in water to produce H⁺ and Cl^– ions. H⁺ ion combines with water molecules to produce hydronium ions.

Question 16.
Which among the following is not a base?
(a) NaOH
(b) KOH
(c) NH₄OH
(d) C₂H₅OH
Answer:
(d) C₂HsOH
Explanation: C₂H₅OH is not a base. C₂H₅OH is an organic compound with -OH functional group that is known as alcohol. It cannot give OH^– ions in its solution. It cannot dissociate ions in a solution. Thus, it cannot be a basic compound.

Question 17.
Identify the correct representation of reaction occurring during the chloralkali process.
(a) 2NaCl_(l) + 2H₂O_(l) → 2NaOH_(l) + Cl_2(g) + H_2(g)
(b) 2NaCl_(l) + 2H₂O_(aq) → 2NaOH_(aq) + Cl_2(g) + H_2(aq)
(c) 2NaCl_(aq) + 2H₂O_(l) → 2NaOH_(aq) + Cl_2(aq) + H_2(aq)
(d) 2NaCl_(aq) + 2H₂O_(l) → 2NaOH_(aq) + Cl_2(g) + H_2(g)
Answer:

Question 18.
Which of the following statements is true for acids?
(a) Bitter and change red litmus to blue.
(b) Sour and change red litmus to blue.
(c) Sour and change blue litmus to red.
(d) Bitter and change blue litmus to red.

Question 19.
Zinc granules on treating with an acid X, form zinc sulphate (ZnSO₄) salt along with the evolution of a gas Y, which burns with a pop sound when brought near to a burning candle. Identify acid X and gas evolved Y.
(a) X-sulphuric acid and Y-oxygen gas
(b) X-hydrochloric acid and Y-oxygen gas
(c) X-sulphuric acid and Y-hydrogen gas
(d) X-hydrochloric acid and Y-hydrogen gas [Diksha]
Answer:
(c) X-sulphuric acid and Y-hydrogen gas

Explanation: When an acid reacts with a metal, hydrogen gas is liberated. In the given reaction, when dilute sulphuric acid reacts with zinc granules, hydrogen gas is liberated and zinc sulphate solution is formed:

The presence of hydrogen gas is tested by bringing a lighted candle near it. When a lighted candle is brought near the test tube containing hydrogen gas, it burns with a ‘pop’ sound making a little explosion.

Hence, acid X is sulphuric acid and gas Y is hydrogen gas.

Question 20.
Which of the following solutions in water does not conduct electricity?
(a) Hydrochloric acid
(b) Sodium chloride
(c) Glucose
(d) Sulphuric acid [Diksha]
Answer:
(c) Glucose

Explanation: The aqueous solution of an acid conducts electricity because of the presence of charged particles called ‘ions’ in it. When hydrochloric acid (HCl) is dissolved in water, its aqueous solution contains hydrogen ions (H⁺) and chloride ions (Cl^–). These ions carry electric currents. So, due to the presence of H⁺ and Cl^– ions, a solution of hydrochloric acid conducts electricity.

On the other hand, the hydrogen-containing compound such as glucose is not categorized as acid because it does not produce hydrogen ions or some other ions when dissolved in water and hence does not conduct electricity. Therefore, the answer is glucose.

Question 21.
Which of the following will turn phenolphthalein pink?
(a) NaOH_(aq)
(b) HCl_(aq)
(c) CH₃COOH_(aq)
(d) H₂O
Answer:

Question 22.
Which one of the following is not a use of washing soda:
(a) Sodium carbonate (washing soda) is used in glass, soap and paper industries.
(b) It is used in the manufacture of sodium compounds such as borax.
(c) Sodium carbonate can be used as a clean¬ing agent for domestic purposes.
(d) It is used for disinfecting water.
Answer:
(d) It is used for disinfecting water.

Explanation: The compound that is used for disinfecting water is bleaching powder. How¬ever, washing soda is used for removing the permanent hardness of water.

Question 23.
The approximate pH values of four salts is given below. Select the row(s) containing the correct information.

(a) Both (I) and (II)
(b) Both (II) and (III)
(c) Both (III) and (IV)
(d) Both (II) and (IV)
Answer:

Question 24.
Zinc granules on treating with a substance X, form a salt sodium zincate along with the evolution of a gas Y which burns with a pop sound when brought near a burning candle. Identify the substance X and gas evolved Y.

Answer:
(b) X is Sodium hydroxide and Y is hydrogen.

Explanation: When zinc granules react with sodium hydroxide, salt sodium zincate is formed along with hydrogen gas, which burns with a pop sound.

The equation of the reaction taking place is:
2NaOH_(aq) + Zn(s) → Na₂ZnO_2(aq) + H_2(g)

Question 25.
Which of the following salts belong to the same family of salts?
(I) sodium chloride and sodium acetate
(II) calcium sulphate, magnesium sulphate
(III) sodium carbonate and sodium hydrogen -carbonate
(IV) sodium chloride and magnesium sulphate
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) (I), (II) and (III)
(d) (I), (III) and (IV)
Answer:

Question 26.
A student noted his observations regarding the acidic or basic nature of salts as below:
(I) Sodium chloride is a neutral salt
(II) Ammonium chloride is a basic salt
(III) Sodium carbonate is a neutral salt
(IV) Copper sulphate is an acidic salt Select the incorrect observations:
(a) Both (I) and (III)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (II) and (IV)
Answer:
(b) Both (II) and (III)

Explanation: The salts of strong acids and strong bases give neutral solutions. Therefore, sodium chloride is a neutral salt as it is obtained from sodium hydroxide (a strong base) and hydrochloric acid (a strong acid).

The salts of strong acids and weak bases give acidic solutions. Therefore, ammonium chloride and copper sulphate are acidic salts as ammonium chloride is obtained from ammonium hydroxide (a weak base) and hydrochloric acid (a strong acid), and copper sulphate is obtained from copper hydroxide (a weak base) and sulphuric acid (a strong acid).

The salts of weak acids and strong bases give basic solutions. Therefore, sodium carbonate is a basic salt as it is obtained from carbonic acid (a weak acid) and sodium hydroxide(a strong base).

Assertion Reasoning questions Class 10 Science Chapter 2

For the following questions, two statements are given – one labelled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both (A) and (R) are true and (R) is the correct explanation of the (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Question 27.
Assertion,(A): HCl gas does not change the colour of dry blue litmus paper.
Reason (R): Acids always produce hydrogen ions.
Answer:
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the (A).

Explanation: HCl gas does not change the colour of dry litmus paper but changes colour of moist litmus paper as acids produce hydrogen ions only in solution.

Question 28.
Assertion (A): Generally, the colour of indicators changes in a particular pH range.
Reason (R): Indicators are weak acids or weak base and exhibit different colours in molecular form and ionic form.
Answer:
(a) (A) and (R) are true and (R) is the correct explanation of the (A).

Explanation: Since indicators are weak acids or weak bases, their percentage of existence in molecular state and in ionized state depends on the strength of acidic/basic/neutral solution to which they are added. Hence their colours change at a particular pH range.

Question 29.
Assertion (A): Zinc reacts with sodium hydroxide solution and hydrogen gas is evolved.
Reason (R): All metals react with bases to evolve hydrogen gas.

Question 30.
Assertion (A): While diluting an acid, water is slowly added to acid with constant stirring.
Reason (R): The process of dissolving an acid in water is a highly exothermic reaction.

Question 31.
Assertion (A): Metal oxides are acidic in nature.
Reason (R): Calcium hydroxide reacts with carbon dioxide to form a salt and water.
Answer:
(d) (A) is false, but (R) is true.

Explanation: The reaction of calcium hydroxide with carbon dioxide to form a salt and water is similar to the reaction between an acid and a base. Therefore, non-metal oxides are acidic in nature.

Question 32.
Assertion (A): When copper sulphate crystals are heated in a dry boiling tube, they turn white.
Reason (R): Water of crystallization is the number of water molecules present in one formula unit of a salt.
Answer:
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).

Explanation: Copper sulphate crystals that seem to be dry contain water of crystallisation. When we heat the crystals, this water is removed and the salt turns white.
CUSO₄.5H₂O → CuSO₄ + 5H₂O

Question 33.
Assertion (A): When copper oxide is added to dilute hydrochloric acid, the colour of the solution becomes blue-green.
Reason (R): Copper (II) chloride is formed.
Answer:
(a) (A) and (R) are true and (R) is the correct explanation of the (A).

Explanation: When copper oxide is added to dilute hydrochloric acid, the colour of the solution becomes blue-green due to the formation of Copper (II) chloride, which is blue-green in colour.

(Competency Based Questions (CBQs))

Question 1.
A chemistry student pLaced a strip of blue litmus paper and a strip of red litmus paper in a glass dish. Then she added a drop of dilute sulphuric acid to each strip of litmus paper. She observed that the blue litmus paper turned red, but the red litmus paper did not change color. Next, she placed a drop of sodium hydroxide (NaOH) on other strips of blue and red litmus paper. This time, the red litmus paper turned blue, but the blue litmus paper did not change. Finally, she put a drop of distilled water on strips of blue and red litmus paper. Neither strip changed color. She repeated the tests several times with the same results. The student concluded that acids turn blue litmus paper red; bases, such as sodium hydroxide, turn red litmus paper blue. As water did not affect either red or blue litmus paper, she reasoned that water was not an acid or a base, but a neutral substance.

Keeping these results in mind, the student poured a little sodium hydroxide into a beaker containing red and blue litmus paper. Then she added hydrochloric acid (HCl) drop by drop until the solution became neutral. She determined that a new, neutral substance had formed in the beaker. The substance was table salt, or sodium chloride (NaCl), which is one of many salts formed from an acid and a base.
(A) If a drop of an unknown substance turns blue litmus paper red, but does not change red litmus paper, what will be the substance – an acid or a base?
Answer:

(B) When strips of blue and red litmus paper are put in a beaker filled with a clear solution, neither litmus paper changes colour. What can you say about the solution?
Answer:
The solution must be neutral.

(C) Based on the results of this experiment, when would salt be formed?
Answer:

(D) What happens when nitric acid is added to egg shell?
Answer:
Calcium carbonate is main component of egg shell so when we add nitric acid to egg shell, it reacts with calcium carbonate to form soluble calcium nitrate and water with brisk effervescence of carbon dioxide gas.
CaCO₃(s) + 2HNO₃(aq) → Ca(NO₃)₂(aq) + CO₂(g) + H₂O

Question 2.
When we smile, our teeth become visible. So, we should ensure that we have a beautiful set of teeth as it makes our smile even more beautiful! Tooth enamel is the thin outer covering of the tooth. This tough shell is the hardest tissue in the human body. Enamel covers the crown which is the part of the tooth that’s visible outside of the gums.

Calcium phosphate is present in tooth enamel. Its nature is:
(a) Basic
(b) Acidic
(c) Neutral
(d) Amphoteric
Answer:
(a) Basic

Explanation: Calcium phosphate Ca₃(PO₄)₂ is a basic salt, as it is formed by the combination of a weak acid (phosphoric acid) and a slightly stronger base (calcium hydroxide).

Question 3.
Patrick read about an industrial process for the electrolysis of sodium chloride solutions.
It is the technology used to produce chlorine and sodium hydroxide which are commodity chemicals required by industry. 35 million tons of chlorine were prepared by this process in 1987. Industrial-scale production began in 1892. Usually, the process is conducted on a brine (an aqueous solution of NaCl), in which case NaOH, hydrogen, and chlorine are formed. When using calcium chloride or potassium chloride, the products contain calcium or potassium instead of sodium. Related processes are known that use molten NaCl to give chlorine and sodium metal or condensed hydrogen chloride to give hydrogen and chlorine.
(A) Name the process referred to in the above passage.
Answer:
The process referred to in the passage is chlor-alkali process because of the products formed – chlor for chlorine and alkali for sodium hydroxide.

(B) Where are the products of the above process produced?
Answer:

(C) Write the chemical equation for the reaction taking place in the process.
Answer:
The chemical equation for the reaction taking place is:
2NaCl(aq) + 2H₂O → 2NaOH(aq) + Cl₂(g) + H₂(g)

(D) How is bleaching powder prepared from one of the products formed in this industrial process?
Answer:

Question 4.
Neetu’s friend suffered a fracture in her foot while riding her bicycle. She had to be admitted to the nursing home and the doctor plastered her foot.

The chemical formula for Plaster of Paris is:
(a) CaSO₄.2H₂O
(b) CaSO₄.H₂O
(c) CaSO₄.\(\frac{1}{2}\)H₂O
(d) 2CaSO₄.H₂O
Answer:
(c) CaSO₄. \(\frac{1}{2}\) H₂O

Explanation: Chemical name of Plaster of Paris is calcium sulphate hemihydrate. It is written in this form because two formula units of CaSO₄ share one molecule of water.

Related Theory
When gypsum is heated at 373K, it loses water molecules.

It is a white powder used by doctors for supporting fractured bones. It is also used for making toys, materials for decoration and for making surfaces smooth.

Question 5.
Sabina studied in history about Mahatma Gandhi’s Dandi March and came to know that sodium chloride was an important symbol in our struggle for freedom. She started exploring from the internet as she was anxious to know what all we can do with this salt other than using it as a table salt to make food tasty. Table salt is also used to preserve food, facilitates transport of nutrients and oxygen and is used as raw material to form various salts.

Based on the understanding of the given passage and the related studied concepts, answer the following questions:
(A) Name two salts of daily use for which common salt (sodium chloride) is the raw material.
(B) Draw a diagram of chloralkali process and write its equation.
Answer:

Question 6.
While performing experiments in chemistry lab, one should always wear a laboratory coat and be very careful while performing experiments. Some students have the bad habit of creating nuisance for other students which distracts the students and may cause serious accidents such as spilling of acid or can cause burn injuries.

If a few drops of concentrated acid accidentally spills over the hand of a student, what should be done?
(a) Wash the hand with a saline solution
(b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate
(c) After washing with plenty of water, apply a solution of sodium hydroxide on the hand
(d) Neutralise the acid with a strong alkali
Answer:
(b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate

Explanation: In such an accident, washing the hands with water will dilute the acid and wash it out. Any remaining acid will be neutralized with sodium hydrogen carbonate (baking soda) as it is a base. This will minimize the effect of damage caused by acid to the skin.

Remember, too strong a base (like NaOH) can be corrosive.

Question 7.
Take about 2 mL of dilute NaOH solution in a test tube and a small amount of copper oxide in a beaker. Add two drops of phenolphthalein solution in the test tube. Add dilute HCl solution in both the test tube and the beaker drop by drop while stirring. Now add a few drops of NaOH to the mixture in the test tube.
(A) When two drops of phenolphthalein solution are added to the test tube,
(a) The solution turns pink in colour
(b) The solution turns colourless
(c) The solution turns red
(d) The solution turns yellow
Answer:
(a) The solution turns pink in colour

Explanation: Phenolphthalein is a colourless reagent which is used as an indicator as it changes the colour to pink in a basic solution. As dilute NaOH is a basic solution, its colour changes to pink on adding a few drops of phenolphthalein solution.

(B) @Four students recorded their observations on adding dilute HCL to the beaker containing copper oxide. Select the correct observation:

Answer:

(C) Select the correct observation(s):
When dilute HCl solution is added to the test tube drop by drop (after adding two drops of phenolphthalein solution) and then a few drops of NaOH solution are added to this mixture:
(I) The solution turns coLourless on adding dilute HCl
(II) The solution turns pink on adding dilute HCl
(III) The solution turns colourless again on adding NaOH to the mixture.
(IV) The solution turns pink again on adding NaOH to the mixture
(a) Both (I) and (III)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (II) and (IV)
Answer:

(D) Identify the option that correctly describes the products formed in the test tube and beaker on adding dilute HCl:

Answer:
(d) Test Tube: Sodium chloride + water; Beaker: Copper chloride + water

Explanation: The products formed in the test is sodium chloride and water and that in beaker is copper chloride and water.

When sodium hydroxide reacts with dilute hydrochloric acid, it forms sodium chloride and water:
When copper oxide reacts with HCl, it forms copper chloride and water:
CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l)

(E) Select the incorrect statement(s):
(I) Reaction of sodium hydroxide with dilute hydrochloric acid is a displacement reaction.
(II) Reaction of copper oxide with dilute hydrochloric acid is a double displacement reaction.
(III) Reaction of sodium hydroxide with dilute hydrochloric acid is a neutralization reaction.
(IV) Reaction of copper oxide with dilute hydrochloric acid is a neutralization reaction.
(a) Only (I)
(b) Only (II)
(c) Both (I) and (IV)
(d) Both (II) and (III)
Answer:
(a) Only (I)

Explanation: Reaction of sodium hydroxide with dilute hydrochloric acid is a neutralization reaction which is also a double displacement reaction as products are formed by the exchange of ions between the reactants.

Similarly, the reaction of copper oxide with dilute hydrochloric acid is also a neutralization reaction which is also a double displacement reaction.

Whereas in a displacement reaction, a more reactive substance displaces a less reactive substance from its compound as in the reaction between a metal such as zinc and dilute hydrochloric acid.

Question 8.
Sumit along with his friend went to a nearby shopping mall. They were standing under a tree when an ant stung his friend on his hands due to which his friend’s hand was painting a lot.

Name the acid along with its chemical formula present in ant sting.
Answer:
The acid present in ant sting is methanoic acid (formic acid). The chemical formula is HCOOH. Explanation: When an ant stings, it leaves formic acid (Methanoic acid) which causes pain and irritation. To get relief from the sting, mild base like baking soda can be applied on the stung.

Question 9.
Take about 1g solid NaCl in a clean and dry test tube and set up the apparatus as shown in Figure.

Add some concentrated sulphuric acid to the test tube.
(A) The gas produced in the test tube is:
(a) Hydrogen
(b) Hydrogen chloride
(c) Hydrogen sulphide
(d) Sulphur dioxide
Answer:
(b) Hydrogen chioride
Explanation: When concentrated sulphuric acid is added to sodium chloride, the following reaction takes place:

2NaCl+ H₂SO₄→ Na₂SO₄ + 2HCl

(B) A student tested the gas coming out of the delivery tube first with dry blue litmus paper and then with wet litmus paper and noted down the following observations. Select the correct observation:

Answer:

(C) If climate is humid, the gas evolved is passed through a guard tube containing:
(a) Calcium hydroxide
(b) Calcium carbonate
(c) Calcium sulphate
(d) Calcium chloride
Answer:
(d) Calcium chloride

Explanation: During the preparation of hydrogen chloride gas, the gas is usually passed through the guard tube containing calcium chloride during humid climate, as calcium chloride is a good drying agent and absorbs moisture from the gas.

(D) Select the incorrect statement(s):
(I) Hydrogen ions in HCl are produced even in absence of water.
(II) Hydrogen ions can exist alone.
(III) Hydrogen ions exist after combining with water molecules.
(IV) Hydrogen ions in HCl are produced only in presence of water
(a) Only (I)
(b) Both (I) and (II)
(c) Both (I) and (III)
(d) Both (II) and (IV)
Answer:
(b) Both (I) and (II)
Explanation: The separation of H⁺ ions from HCl molecules cannot occur in the absence of water.
HCl +H₂O → H₃O⁺ + Cl^–
Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H⁺(aq) or hydronium ion (H30⁺).
H⁺ + H₂O → H₃O⁺

(E) Hydrogen ions must always be shown as H⁺(aq) or hydronium ion (H₃0⁺) as:
(a) Hydrogen ions combine with water to form hydronium ions
(b) Hydrogen gas dissociates into ions.
(c) All acids dissociate into hydrogen ions in presence of a base.
(d) Hydrogen ions separate from acids on passing electricity.
Answer:

Question 10.
Acids and bases represent two important classes of chemical compounds. In every day life, acids and bases play a role in everything from the digestion of the foods you eat to the function of the medicine you take and even the cleaning products you use. Without acids and bases, many of the products in your home today would not have much use. Acids and bases are also important in atmospheric, geological, and physiological processes because they have unique chemical properties. Acids and bases have unique chemical properties because of the atomic composition of these compounds and how these compounds interact with other atoms and molecules.
The pH of some common substances is shown below:
(A) The nature of calcium phosphate present in tooth enamel is:
(a) Basic
(b) Amphoteric
(c) Acidic
(d) Neutral
Answer:

(B) What is the pH value of saliva after meal?
(a) between 0 and 4
(b) between 4 and 5
(c) between 5 and 6
(d) between 6 and 7
Answer:
(c) between 5 and 6

Explanation: The pH of saliva after meals is around 5.8 due to the increased activity of bacteria on the food that we eat.

(C) Given below are four statements. Select the incorrect statement(s):
(I) Pain and irritation during indigestion is due to the excess acid produced by the stomach.
(II) People use antacids to get rid of this pain which are bases.
(III) Milk of magnesia is an antacid as it is a mild acid.
(IV) Antacids neutralize the excess acid produced in the stomach.
(a) Only (I)
(b) Only (II)
(c) Only (III)
(d) (III) and (IV)
Answer:
(c) Only (III)

Explanation: Antacids are bases which help in getting rid of the pain and irritation during indigestion by neutralizing the excess acid produced in the stomach. Milk of magnesia or magnesium hydroxide is a mild base that is used as an antacid.

(D) The pH level of the human body is:
(a) Less than 7, acidic
(b) Equal to 7, Neutral
(c) More than 7, basic
(d) None of the above
Answer:

(E) A student tabulated the naturally occurring acidic substances and the acid contained in them.

Select the option containing the correct acid found in them:
(a) Both (I) and (II)
(b) Both (III) and (IV)
(c) Both (II) and (IV)
(d) Both (I) and (III)
Answer:
(b) Both (III) and (IV)

Explanation: Vinegar contains acetic acid, whereas nettle sting contains methanoic acid.

Question 11.
If you think the best way to put out a fire is by dousing it with water, you’d be surprised to know you’re wrong. As it turns out, not all fires are created equal, and there is more than one way to extinguish them safely. There are situations where you should not use water to deal with a fire at all. For example, an electrical fire.

Name the chemicals used in acid fire extinguishers and the gas that evolved from it when it is used?
Answer:
The chemicals used in soda acid fire extinguishers are sodium hydrogen carbonate and sulphuric acid.
The gas evolved when the two reactants react is carbon dioxide which is used for extinguishing electrical fires.
The reaction taking place between the two chemicals is
2NaHCO₃ + H₂SO₄ → Na₂SO₄ + 2CO₂ + 2H₂O

Question 12.
The reaction between MnO₂ with HCl is depicted in the following diagram. It was observed that a gas with bleaching abilities was released.

(A) The chemical reaction between MnO₂ and HCl is an example of:
(a) displacement reaction
(b) combination reaction
(c) redox reaction
(d) decomposition reaction.
Answer:
(c) redox reaction

Explanation: When MnO₂ reacts with HCl, the following reaction takes place in which chlorine gas is also evolved, which has bleaching properties.
MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O

In this reaction, Hydrochloric acid is oxidized to chlorine and Manganese dioxide is reduced to manganese dichloride. As both oxidation and reduction are taking place in this reaction, it is a redox reaction.

(B) Chlorine gas reacts with ……………… to form bleaching powder.
(a) dry Ca(OH)₂
(b) dil. solution of Ca(OH)₂
(c) cone, solution of Ca(OH)₂
(d) dry CaO
Answer:
(a) dry Ca(OH)₂
Explanation: Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2],
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

(C) Identify the correct statement from the following:
(a) MnO₂ is getting reduced whereas HCl is getting oxidized
(b) MnO₂ is getting oxidized whereas HCl is getting reduced.
(c) MnO₂ and HCl both are getting reduced.
(d) MnO₂ and HCl both are getting oxidized.
Answer:
(a) Mn02 is getting reduced whereas HCl is getting oxidized.
Explanation: In the reaction between
MnO₂ and HCl, MnO₂ is getting reduced to manganese dichloride as it is losing oxygen atoms. Whereas, HCl is getting oxidized to chlorine by the removal of oxygen.

Related Theory
Oxidation is the addition of oxygen to a substance or the removal of hydrogen from a substance.
Reduction is the addition of hydrogen to a substance or removal of oxygen from a substance.
The oxidising agent is the substance that provides oxygen for oxidation or which removes hydrogen.
Reducing agent is the substance which provides hydrogen for reduction or which removes oxygen.

(D) In the above-discussed reaction, what is the nature of MnO₂?
(a) Acidic oxide
(b) Basic oxide
(c) Neutral oxide
(d) Amphoteric oxide
Answer:
(b) Basic oxide
Explanation: As MnO₂ reacts with HCl to form salt, water and chlorine gas, it is a basic oxide since it reacts with an acid. Moreover, oxides of metals are basic in nature whereas oxides of non-metals are acidic in nature.

(E) What will happen if we take dry HCl gas instead of aqueous solution of HCl?
(a) Reaction will occur faster.
(b) Reaction will not occur.
(c) Reaction rate will be slow
(d) Reaction rate will remain the same.
Answer:
(b) Reaction wiil not occur

Explanation: A substance shows its acidic properties only in presence of water as it is able to dissociate into H+ ions, which is responsible for its acidic properties.

So, if we use dry HCl, then no reaction will take place as HCl will not be able to dissociate into ion$ as shown by the following reaction:
HCl + H₂O H₃O⁺ + Cl^–

Question 13.
Frothing in Yamuna:
The primary reason behind the formation of the toxic foam is high phosphate content in the wastewater because of detergents used in dyeing industries, dhobi ghats and households. Yamuna’s pollution level is so bad that parts of it have been labelled ‘dead’ as there is no oxygen in it for aquatic life to survive.

(A) Predict the pH value of the water of river Yamuna if the reason for froth is high content of detergents dissolved in it.
(a) 10-11
(b) 5-7
(c) 2-5
(d) 7
Answer:
(a) 10-11

Explanation: Detergents are basic in nature having pH value of 10-11. As the froth has a high content of detergents dissolved in it, the pH value of water of river Yamuna will be 10 -11.

(B) Which of the following statements is correct for the water with detergents dissolved in it?
(a) low concentration of hydroxide ion (OH^–)and high concentration of hydronium ion (H₃O⁺)
(b) high concentration of hydroxide ion (OH^–) and low concentration of hydronium ion (H₃O⁺)
(c) high concentration of hydroxide ion (OH^–) as well as hydronium ion (H₃O⁺)
(d) equal concentration of both hydroxide ion (OH^–) and hydronium ion (H₃O⁺).
Answer:
(b) high concentration of hydroxide ion (OH^–) and low concentration of hydronium ion (H₃O⁺)

Explanation: As detergents are basic in nature, the concentration of hydroxide ions will be high and the concentration of hydronium ions will be less.

Related Theory
When bases are dissolved in water, they dissociate into hydroxide ions.
For example, NaOH(aq) → Na⁺(aq) + CH^–(aq)
KOH(aq) → K⁺(aq) + OH^–(aq)

(C) The table provides the pH value of four solutions P, Q, R and S

Which of the following correctly represents the solutions in increasing order of their hydronium ion concentration?
(a) P > Q > R> S
(b) P > S > Q > R
(c) S < Q < R< P
(d) S < P < Q < R
Answer:
(c) S < Q < R. < P

Explanation: The pH of a substance is related to the concentration of hydrogen or hydronium ions. An acid has a high concentration of hydronium ions and a low pH value whereas a base has a high pH value and a low concentration of hydronium ions.

So, we can say, lower the pH value, the more is the concentration of hydronium ions. Therefore, the hydronium ion concentration is least in S, followed by Q, R and then P which has the maximum concentration of hydronium ions.

(D) High content of phosphate ion in river Yamuna may lead to:
(a) decreased level of dissolved oxygen and increased growth of algae
(b) decreased level of dissolved oxygen and no effect of the growth of algae
(c) increased level of dissolved oxygen and increased growth of algae
(d) decreased level of dissolved oxygen and decreased growth of algae
Answer:
(a) decreased level of dissolved oxygen and increased growth of algae

Explanation: When the amount of phosphate ions in water increases, it leads to decreased level of dissolved oxygen which is harmful for the aquatic organisms. This leads to an increased growth of algae due to presence of nutrients.

Related Theory
Eutrophication is the process in which a water body becomes overly enriched with nutrients, leading to plentiful growth of simple plant life. The excessive growth (or bloom) of algae and plankton in a water body are indicators of this process.

(E) If a sample of water containing detergents is provided to you, which of the following methods will you adopt to neutralize it?
(a) Treating the water with baking soda
(b) Treating the water with vinegar
(c) Treating the water with caustic soda
(d) Treating the water with washing soda
Answer:
(b) Treating the water with vinegar

Explanation: As detergents are basic in nature, an acid will neutralize it. Out of the substances mentioned, only vinegar is acidic, as it is 5 – 8% solution of ethanoic acid in water.

Very Short Answer Type Questions

Question 1.
What types of ions are formed: (a) when an acid is dissolved in water (b) when a base is dissolved in water?
Answer:

Question 2.
‘A’ is a soluble acidic oxide and ‘B’ is a soluble base. Compared to pH of pure water, what will be the pH of (a) solution of A (b) solution of B?
Answer:
pH of pure water is 7. As A is a soluble acid, its pH will be less than that of pure water whereas pH of B will be more than that of pure water as it is a soluble base.

Question 3.
When electricity is passed through a common salt solution, sodium hydroxide is produced along with the liberation of two gases “X” and “Y”. “X” burns with a pop sound whereas “Y” is used for disinfecting drinking water. Identify X and Y.
Answer:
The reaction is chlor-alkali process. As X burns with a pop sound, X is hydrogen gas. Y is chlorine gas which is used for disinfecting drinking water.

Question 4.
Which bases are called alkalis? Give one example of alkali.
Answer:
The bases that are soluble in water are called alkalies. One example of an alkali is sodium hydroxide, NaOH.

Question 5.
Name the acid and base that have com stituted the salt ammonium nitrate
Answer:

Question 6.
Oxides of metals are basic while those of non-metals are acidle, Explain.
Answer:
Oxides of metals are basic as they react with acids to produce salt and water.
CuO + 2HCl → CuCl₂ + H₂O
Oxides of non-metals are acidic as they react with bases to produce salt and water.
CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Question 7.
Write a balanced chemical eauatin for the renction between sodium carbonals and hydrochloric acid indicating the physical state of reactions and the products.
Answer:
The balanced equation for the reaction between sodium carbonate and hydrochloric acid is given below:
Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)

Question 8.
Give reasons for the following:
(A) Only one half of water molecule is shown in the formula of Plaster of Paris.
(B) Sodium hydrogen carbonates is used as an antacid.
(C) On strong heating, blue coloured copper sulphate crystals turn white.
Answer:

Question 9.
A student prepared solutions of (I) an acid and (II) a base in two separate beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since, both the solutions are colourless, how will she distinguish between the two?
Answer:
In the absence of litmus, other natural or synthetic substances can be used to test acid and bases. Such substances are called indicators. Indicators such as methyl orange and phenolphthalein can be used to test the nature of a solution.

These indicators show change in their colour in acidic, neutral and basic solutions. We can also use natural indicators such as turmeric and grape juice. A few indicators with characteristic colour change are shown below:

Question 10.
Fill in the missing data in the given table.


Answer:

1. Acid: HCl
NH₄OH + HCl → NH₄Cl + H₂O

2. Formula: CuSO₄ and base: Cu(OH)₂
H₂SO₄ + Cu(OH)₂ → CuSO₄ + 2H₂O

3. Acid: HCl
NaOH + HCl → NaCl + H₂O

4. Base: Mg(OH)₂
Mg(OH)₂ + 2HNO₃ → Mg(NO₃)₂ + 2H₂O

5. Base: KOH and Acid: H₂SO₄
2KOH + H2SO₄ → K2SO₄ + 2H₂O

6. Acid: HNO₃
Ca(OH)₂ + 2HNO₃ → Ca(NO₃)₂ + 2H₂O

Question 11.
How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water that can be removed by it?
Answer:

Question 12.
(A) You are given two solutions A and B and their pH is 6 and 8 respectively. Answer the following:
(i) Which of the two solutions have more hydrogen ion concentration?
(ii) Which is acidic and which is basic?
Answer:
pH of solution A = 6 pH of solution B = 8
(i) Solution A will have a higher hydrogen ion concentration. Explanation: We know that the pH of any solution is inversely proportional to the hydrogen ion concentration. This means that the solution that has lower pH number will have the higher hydrogen ion concentration.

(ii) Also solution A is acidic and solution B is basic because H+ ion concentration is higher in acidic solution.

(B) What is dilution?
Answer:
Mixing an acid or base with water results in decrease in concentration of ions (H₃O⁺/ OH^–) per unit volume. Such process is called dilution and the acid or base is said to be dituted. The process of dissolving an acid or a base in water is a highly exothermic reaction.

Question 13.
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?
Answer:

Question 14.
Crystals of a substance changes their color on heating in a closed vessel but regained it after sometime, when they were allowed to cool down.
(A) Name one such substance.
Answer:
One such substance whose crystals changes its colour from blue to white on heating in a closed vessel for some time is hydrated copper sulphate, CuSO₄.5H₂O.

(B) Explaain the phenomenon involved.
Answer:
Hydrated salts contain molecules of water known as water of crystallization. When such crystals are heated in a closed container, they lose their water of crystallization and hence change of colour is observed.

Related Theory:
When a salt which has lost its water of crystallization due to heating is left to cool down, it absorbs moisture from air and regains its water of crystallisation and thus, also its color.

Question 15.
The pH of the mouth of a person is lower than 5.5. What changes will occur in EMB his mouth? How these changes can be controlled? Write any two measures.
Answer:
When the pH of the mouth of a person is lower than 5.5, the acid produced by the action of bacteria on sugar and food particles in mouth corrodes even the tooth enamel which is made up of calcium phosphate. This leads to dental caries and tooth decay.

These changes can be controlled by the following measures:

1. By using tooth pastes, which are generally basic in nature, as they can neutralize the excess acid produced in the mouth and hence help in preventing tooth decay.
2. By regular brushing of teeth twice a day and especially after eating sweets and chocolates.

MCQ Questions for Class 10 Science with Answers

Class 10 Science Chemistry MCQ:

• Chemical Reactions and Equations Class 10 MCQ
• Acids, Bases and Salts Class 10 MCQ
• Metals and Non-metals Class 10 MCQ
• Carbon and Its Compounds Class 10 MCQ
• Periodic Classification of Elements Class 10 MCQ

Class 10 Science Chemistry Chapter 3 MCQ With Answers

Chemistry Class 10 Chapter 3 MCQs On Metals and Non-metals

Metals And Non Metals Class 10 MCQ Question 1.
Which of the following properties is generally not shown by metals?
(a) Electrical conduction
(b) Sonorous in nature
(c) Dullness
(d) Ductility
Answer:
(c) Dullness

Explanation: Metals generally do not show dullness. Metals such as gold and silver are usuaLly shiny rather than dull.

Related Theory:
Conduction: Metals are good conductors of heat and electricity as they have free electrons. Silver and copper are the best conductors of heat, whereas lead and mercury are poor conductors of heat. Sonorous: Metals that produces a sound on striking a hard surface.

Metallic lustre: Metal, in its pure state, has a shining surface. This property is known as metallic lustre. Ductility: The ability of metals to be drawn into thin wires. Cold is the most ductile metal.

Metal And Non Metals Class 10 MCQ Question 2.
The solution of one of the following compounds will not conduct electricity. This compound is:
(a) NaCl
(b) CCl₄
(c) MgCl₂
(d) CaCl₂
Answer:

Metals And Nonmetals Class 10 MCQ Question 3.
Which one of the following metals does not react with cold as well as hot water?
(a) Na
(b) Ca
(c) Mg
(d) Fe
Answer:

Class 10 Metals And Non Metals MCQ Question 4.
An aluminium strip is kept immersed in freshly prepared ferrous sulphate solution taken in a test tube, the change observed is that:
(a) Green solution slowly turns colourless
(b) Lower end of test tube becomes slightly warm
(c) A colourless gas with the smell of burning sulphur is observed
(d) Light green solution changes to blue
Answer:

Class 10 Science Chapter 3 MCQ Question 5.
Which of the following oxide(s) of iron would be obtained on the prolonged reaction of iron with steam?
(a) FeO
(b) Fe₂O₃
(c) Fe₃O₄
(d) Fe₂O₃ and Fe₃O₄
Answer:
(c) Fe₃O₄

Metals And Non Metals MCQ Question 6.
What happens when calcium is treated with water?
(I) It does not react with water.
(II) It reacts violently with water.
(III) It reacts Less violently with water.
(IV) Bubbles of hydrogen gas formed stick to the surface of calcium.
(a) (I) and (IV)
(b) (II) and (III)
(c) (I) and (II)
(d) (III) and (IV)
Answer:
(d) (III) and (IV)

Explanation: When calcium is treated with water, it reacts vigorously with water and to produce a cloudy white precipitate of calcium hydroxide and hydrogen gas is released as bubbles.

‘Related Theory
Sometimes hydrogen bubbles get stuck to the surface of calcium metaL making it tight arid thus calcium starts floating. Reaction of calcium with water is exothermic but the heat produced in this reaction is not sufficient so that hydrogen can catch

Ch 3 Science Class 10 MCQ Question 7.
Which of the foLLowing are not ionic compounds?
(I) KCl
(II) HCl
(III) CCl₄
(IV) NaCl
(a) (I) and (II)
(b) (II) and (III)
(c) (III) and (IV)
(d) (I) and (III)
Answer:

Class 10 Science Ch 3 MCQ Question 8.
Generally, non-metals are not Lustrous. Which of the following non-metals is lustrous?
(a) Sulphur
(b) Oxygen
(c) Nitrogen
(d) Iodine
Answer:
(d) Iodine

Explanation: Iodine is a non-metal with a lustrous appearance and exists in solid state.

Related Theory
Graphite is another non-metaL that is shiny and Lustrous.

MCQ On Metals And Non Metals Class 10 Question 9.
2 mt each of conc. HCL, HNO₃, and a mixture of conc. HCL and conc. HNO₃ in the ratio of 3:1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metaL got dissolved in test tube C. The metal could be:
(a) Al
(b) Au
(c) Cu
(d) Pt

Metal And Non Metals MCQ Class 10 Question 10.
An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept ¡n open air. It reacts vigorously with water. Identify the element from the following:
(a) Mg
(b) Na
(c) P
(d) Co
Answer:
(b) Na

Explanation: Na (sodium) possesses all the above properties. It is too soft and can be cut with a knife. It is also very reactive and reacts with oxygen or moisture present in air and produces sodium hydroxide, which is a highly exothermic reaction producing a lot of heat. It also reacts with water and burns due to the vigorous formation of hydrogen gas. That is why sodium is stored in kerosene oil to prevent any reaction.

MCQ On Metals And Non Metals Question 11.
Which among the following statements is incorrect for magnesium metal?
(a) It burns in oxygen with a dazzling white flame.
(b) It reacts with cold water to form magnesium oxide and evolves hydrogen gas.
(c) It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas.
(d) It reacts with steam to form magnesium hydroxide and evoLves hydrogen gas.
Answer:

Metal And Non Metal Class 10 MCQ Question 12.
The electronic configurations of three elements X, Y and Z are X – 2, 8; Y – 2, 8, 7 and Z – 2, 8, 2. Which of the following ¡s correct?
(a) X is a metal
(b) Y is a metaL
(c) Z ¡s a non-metal
(d) Y is a non-metaL and Z is a metaL

MCQ Questions For Class 10 Science Chapter 3 Question 13.
In the given reaction,
Al₂O₃ + NaOH → X + H₂O.
What is element X?
(a) NaAlO₂
(b) Na₃Al
(c) Na₂O₃
(d) NaAl₂O₃ [Diksha]

MCQ Of Metal And Nonmetal Class 10 Question 14.
Sandhya took three beakers A, B and C containing zinc sulphate, silver sulphate and iron(ll) sulphate solutions respectively. Copper pieces were added to each beaker. The solution will appear blue in the case of:
(a) Beaker A
(b) Beaker B
(c) Beaker C
(d) Beakers B and C [Diksha]
Answer:
(b) Beaker B

Explanation: The solution will appear blue in Beaker B. Let us see how.

When pieces of copper metal are kept immersed in silver sulphate solution for some time, the solution gradually becomes blue and a shiny greyish-white deposit of silver metal is formed on the copper strip.

In this reaction, copper metal is displacing silver from silver sulphate solution, forming copper sulphate and silver metal. The solution becomes blue due to the formation of copper sulphate. The reason behind this displacement reaction is that copper is more reactive than silver.

On the other hand, copper metal is less reactive than iron and zinc and hence cannot displace them from their respective salt solutions.

Chapter 3 Science Class 10 MCQ Question 15.
Arrange the following metal in the decreasing chemical activity series.
(I) Potassium
(II) Magnesium
(III) Gold
(IV) Iron
Correct options are:
(a) (I), (II), (III) and (IV)
(b) (I), (III), (IV) and (II)
(c) (I), (II), (IV) and (III)
(d) (I), (IV), (II) and (III)

Question 16.
Which metal can be displaced by copper from Its salt solution?
(I) Silver
(II) Magnesium
(III) iron
(IV) Iron
Correct options are:
(a) (I) and (II)
(b) (I) and (III)
(c) (II) and (III)
(d) (I) and (IV)
Answer:
(d) (I) and (IV)

Silver and mercury are less reactive than copper and as copper will displace those metals from its salt solution which are less reactive than it, the correct option is (d).

Question 17.
Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?
(I) Au
(II) Cu
(III) Na
(IV) K
(a) (I) and (II)
(b) (IV) and (III)
(c) (II) and (III)
(d) (II) and (IV)
Answer:
(a) (I) and (II)

Explanation: Gold (Ag) and copper (Cu) obtained after extraction are in impure form. So, metals Au (gold) and Cu (copper) are refined by electrolytic refining. Other than gold and copper, electrolytic refining is used for metals such as Zn and Ag. Sodium (Na) and potassium (K) are extracted by electrolytic reduction. Metals obtained after electrolytic reduction are in pure form.

Related Theory
Alkali metals are very reactive, so they cannot be refined with the help of the electrolytic refining process.

Question 18.
Galvanisation is a method of protecting iron from rusting by coating it with a thin layer of:
(a) Gallium
(b) Aluminium
(c) Zinc
(d) Silver
Answer:
(c) Zinc

Explanation: Zinc (Zn) metal is used to protect iron surfaces from rusting.

Related Theory
Galvanization is basically coating iron or steel with a layer of zinc to prevent it from rusting. Water pipes are also galvanized to prevent corrosion.

Question 19.
Stainless steel is a very useful material in our life, in stainless steel, iron is mixed with:
(a) Mi and Cr
(b) Cu and Cr
(c) Mi and Cu
(d) Cu and Au
Answer:
(a) Ni and Cr

Explanation: Stainless steel is an alloy of iron (74%), nickel (8%) and chromium (18%).

Related Theory
‘Alloying elements enhance the structure and properties such as durability, strength and toughness of the metal. It makes them corrosion-resistant.

Question 20.
If copper is kept in the open air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of:
(a) CuSO₄
(b) CuCO₃
(c) CU(NO₃)₂
(d) CuO
Answer:

Question 21.
Which of the following metals are obtained by electrolysis of their chlorides in a molten state?
(I) Na
(II) Ca
(III) Fe
(IV) Cu
(a) (I)and(IV)
(b) (III) and (IV)
(c) (I) and (III)
(d) (I) and (II)
Answer:

Question 22.
An electrolytic cell consists of:
(I) Positively charged cathode
(II) Negatively charged anode
(III) Positively charged anode
(IV) Negatively charged cathode
(a) (I) and (II)
(b) (III) and (IV)
(c) (I) and (III)
(d) (II) and (IV)
Answer:
(b) (III) and (IV)

Explanation: There is a positively charged anode and a negatively charged cathode in an electrolytic cell. Positively charged ions (cations) are deposited at the negatively charged cathode. Negatively charged ions (anions) are deposited at the positively charged anode.

Question 23.
During electrolytic refining of zinc, it gets:
(a) Deposited on the cathode
(b) Deposited on the anode
(c) Deposited on the cathode as well as anode
(d) Remains in the solution
Answer:

Question 24.
Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following alloys contains non-metal as one of its constituents?
(a) Brass
(b) Bronze
(c) Amalgam
(d) Steel
Answer:
(d) Steel

Explanation: SteeL contains non-metal as one of its constituents. Steel is an alloy made by combining iron and other elements, mainly carbon. Carbon gives strength to iron. It is used to make buildings, ships, automobiles, machines, and appliances.

Related Theory

• Brass – Copper and zinc
• Bronze – Copper and tin
• Amalgam – Mercury with other metal
• Steel – Iron with carbon

Question 25.
Which among the following alloys contains mercury as one of its constituents?
(a) Stainless steel
(b) Alnico
(c) Solder
(d) Zinc amalgam
Answer:

Question 26.
Which one of the following figures correctly describes the process of electrolytic refining?

Answer:

Explanation: In the electrolytic refining process, impure metal forms the anode, which is the positive electrode, whereas pure metal forms the cathode which is the negative electrode.

Figure (c) shows the process of electrolytic refining of copper metal. Copper from impure anode dissolves into the solution. Copper ions (Cu²⁺) from the solution are deposited on the cathode and impurities settle down below the anode as anode mud.

Question 27.
Select the incorrect statements):
(I) Solder is an alloy of lead and copper
(II) Solder is an alloy of lead and tin
(III) Melting point of solder is low
(IV) Melting point of solder is high
(a) Only (I)
(b) Both (I) and (III)
(c) Both (II) and (IV)
(d) Both (I) and (IV)
Answer:

Question 28.
All ionic compounds:
(a) Have high melting point but the low boiling point
(b) Are generally soluble in kerosene
(c) Are generally brittle
(d) Conduct electricity in solid-state
Answer:

Question 29.
The cations and anions present in aluminium oxide are:

Answer:
(b) Cation: Al³⁷; Anion: O^2-

Explanation: Aluminium oxide or Al₂O₃ is formed by the transfer of electrons from aluminium atoms to oxygen atoms.

Aluminium (Atomic number = 13) has 3 valence electrons whereas oxygen (atomic number = 8) has 2 valence electrons.

So, each aluminium atom donates its 3 valence electrons to the oxygen atoms and forms cations [Al³⁺], whereas each oxygen atom gains two electrons and forms anions [O^2-].

Question 30.
The metals which have very low melting points are:
(a) Gallium and caesium
(b) Gallium and sodium
(c) Caesium and potassium
(d) Sodium and potassium

Assertion Reasoning questions Class 10 Science Chapter 3

For the following questions, two statements are given – one labelled Assertion (A) and other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Question 31.
Assertion (A): Alkali metals like sodium and potassium can be cut with a knife.
Reason (R): They have high densities.
Answer:
(c) (A) is true but (R) is false.

Explanation: Alkali metals like sodium and potassium are so soft that they can be cut with a knife as they have low densities.

Question 32.
Assertion (A): Magnesium is less reactive than sodium.
Reason (R): Sodium reacts more vigorously with oxygen than magnesium.
Answer:

Question 33.
Assertion (A): In the following reaction between calcium and water, calcium starts floating.
Ca + 2H₂O → Ca(OH)₂ + H₂
Reason (R): Calcium hydroxide is lighter than water.
Answer:
(c) (A) is true but (R) is false.

Explanation: In the reaction between calcium and water, calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of calcium metal.

Question 34.
Assertion (A): Hydrogen gas is evolved when a metal reacts with nitric acid.
Reason (R): Nitric acid is a strong oxidizing agent.
Answer:

Question 35.
Assertion (A): The compound MgCl₂ will not conduct electricity in a solid-state.
Reason (R): Movement of ions in ionic compounds is not possible in solid-state.
Answer:
(b) Both (A) and (R) are. true but (R) is not the correct explanation of the (A).

Explanation; The compound MgCl₂ is an ionic compound as it is formed by the transfer of electrons between magnesium and chlorine. It will not conduct electricity in solid-state as the movement of ions in ionic compounds is not possible in a solid-state.

Question 36.
Assertion (A): The metals and alloys are good conductors of electricity.
Reason (R): Bronze Is an alloy of copper and tin and it is not a good conductor of electricity.
Answer:
(d) (A) is false but (R) is true.

Explanation: All the metals and alloys are not always good conductors of electricity like bronze is not a good conductor of electricity, its constituents are copper and tin. Copper is a good conductor whereas tin is not a good conductor of electricity. Alloy nichrome is a good conductor of electricity.

Related Theory

• Metals are good conductors of electricity because they.
• have a large number of free electrons.
• Possess small resistivity in the range of 10-8 W m to 10-6 W m. Whereas alloys have more resistivity.

(Competency Based Questions (CBQs))

Question 1.
The exact date that humans first began to mine gold is unknown, but some of the oldest known gold artefacts were found in the Varna Necropolis in Bulgaria. The graves of the necropolis were built between 4700 and 4200 BC, indicating that gold mining could be at least 7000 gears old. In the area of the Kolar Gold Fields in Bangarpet Taluk, Kolar District of Karnataka state, India, gold was first mined prior to the 2nd and 3rd century AD by digging small pits. (Golden objects found in Harappa and Mohenjo-daro have been traced to Kolar through the analysis of impurities — the impurities include 11% silver concentration, found only in KGF ore.

In nature, aluminium is found in a combined state whereas silver/gold is found in Freestate. Give reason.
Answer:
Silver and gold are least reactive metals and are often found in their native or free state. Aluminium is a very reactive metal and is never found in free state, but in combined state.

Question 2.
Dhanteras, also known as Dhanatrayodashi, is the first day that marks the festival of Diwali in India. Dhanteras is the worship of lord Dhanvantari. Fundus considers this an extremely auspicious day for making new purchases, especially of gold or silver articles and new utensils. It is believed that new “Dhan” (wealth} or some item made of precious metal is a sign of good. luck. In modern times, Dhanteras has come to be known as the most: auspicious occasion for buying gold, silver, and other metals, especially kitchenware. Palak, along with her mother, purchased some kitchenware articles made of stainless steel on this occasion.

How does alloying of iron change its properties?
Answer:
Pure iron is very soft arid stretches easily when hot but if iron ismixed with a small amount of carbon (about 0.05 %), it becomes hardand strong. When iron is mixed with nickel and chromium, we getstainless steel, which is hard and does not rust. Thus, if iron is mixedwith some other substance, its properties change.

Question 3.
Have you ever imagined what would happen if all the electrical wires used in our homes, offices and other places were without any covering? Well, people handling them would die of electrical chock and there would be short-circuiting leading to electrical fires all around us!

Electrical wires have a coating of an insulating material. The material, generally used is:
(a) Sulphur
(b) Graphite
(c) PVC
(d) All can be used
Answer:
(c) PVC

Explanation: An insulating substance is required to coat the electrical wire such as PVC, PVC is a polymer and a bad conductor of electricity, it is the most common insulating material used to insulate electrical conductors from electric charge, thus preventing direct human contact with electricity.

Graphite is a good conductor of electricity. Hence, it cannot be used as insulating material. Sulphur, although a bad conductor of electricity, is brittle in nature. So, it cannot be used as an insulating material.

Question 4.
Analyse the following reactivity series given below and answer the questions that follow:

(A) Which of the two metals is more reactive: copper or silver?
Answer:

(B) What will happen if a strip of zinc is immersed in o solution of copper sulphate?
Answer:
When a strip of zinc metal is put in copper sulphate solution, then the blue colour of copper sulphate solution fades gradually and red-brown coating of copper is deposited on zinc strip.

This is an example of displacement reaction.

Explanation: Zinc is more reactive than copper so it will displace copper from its salt solution so displacement reaction takes place.

(C) If copper is kept open in air, it slowly Loses its shining brown surface and gains a green coating. It is due to the formation
(a) Acidic CuSO₄
(b) Basic CuCO₃
(c) Acidic Cu(NO₃)₂
(d) Basic CuO
Answer:

(D) Which one of the following four metals would be displaced from the soLution of its softs by other three metals?
(a) Mg
(b) Ag
(c) Zn
(d) Cu
Answer:
(b) Ag

Explanation: Least reactive metal can be displaced from its solution by other three metals. Silver is least reactive out of the given four metals.

Related Theory
Basic copper carbonate is an undesired layer formed on the surface of the copper and the process is known as corrosion.

Question 5.
Aqua regia is a yellow-orange (sometimes red) fuming liquid, so named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals.

The composition of aqua-regia is:

Answer:

Explanation: Aqua-regia is a mixture of concentrated hydrochloric acid and concen¬trated nitric acid in the ratio of 3:1. Aqua-regia, being a strong acid, dissolves gold.

Question 6.
Atoms that gain electrons and therefore have a net negative charge are known as anions. Conversely, atoms that lose electrons and therefore have a net positive charge are called cations. Cations tend to be metals, while anions tend to be non-metals. Ions may also be single atoms or multiple, complex groups of atoms. When we talk about ions, it’s true that opposites attract.

The opposite negative and positive charges of the ions hold together in ionic bonds, forming ionic compounds, which are just what they sound like: compounds made of ions. The loss or gain from one atom matches the loss or gain of the other, so one atom essentially ‘donates’ an electron to the other atom it pairs up with. Two positive or two negative ions will not join together because they have the same charge. But one positive and one negative will happily join together to make an ionic compound.
(A) Explain the formation of MgO. (Atomic No. of O = 8, Mg = 12).
Answer:
Electronic configuration of Mg: 2, 8, 2 and that of O: 2, 6.
Magnesium atom loses its two valence electrons to form Mg²⁺ ion and oxygen atom gains two electrons to form O₂ ion thereby achieving their nearest inert gas configuration.

(B) Will the aqueous solution of MgO conduct electricity? If yes, give reasons for your answer?
Answer:

(C) Name a solvent in which ionic compounds are soluble and a solvent in which they are insoluble.
Answer:
Ionic compounds are soluble in water and insoluble in kerosene.

(D) Why do ionic compounds have high melting and boiling points?
Answer:

Question 7.
When Rohan was suffering from fever, the doctor had asked his parents to check his temperature every 2 hours and also to keep a record. He was a thermometer that has a certain metal in a liquid state inside it

Generally, metals are soLid in nature. Which one of the following metals is found in Liquid state at room temperature?
(a) Na
(b) Fe
(c) Cr
(d) Hg
Answer:
(d) Hg

Explanation: At room temperature, mercury (Hg) is the only metal found in a liquid state.

Related Theory
All other metals are solid at room temperature. Hg also has the lowest melting point.

Question 8.
Collect the samples of the following metals aluminium, copper, iron, lead, magnesium, zinc and sodium. Hold each of the samples above with a pair of tongs and try burning over a flame. It would be better if students wear eye protection and perform this activity with assistance from the teacher. Repeat with the other metal samples.
(A) Select the incorrect statements).
(I) All metals burn easily.
(II) Not all metals burn easily.
(III) Magnesium burns easily.
(IV) Copper and aluminium take time to burn.
(a) Only (I)
(b) Only (II)
(c) Both (I) and (III)
(d) Both (II) and (IV)
Answer:

(B) The student performing this activity noted the following observations on the colour of flame observed when the metal is burnt.

Select the correct observation.
Answer:
(d) Metal: Magnesium; Colour of Flame: White

Explanation: The colour of flame observed when the given metals are heated is given below:
Aluminium: Silvery white
Copper: Blue
Sodium: Yellow
Magnesium: White

(C) The correct arrangement of metaLs Al, Mg, Na and Zn in the decreasing order of their reactivity towards oxygen ¡s:
(a) Na > Al > Mg > Zn
(b) Na > Mg > Al> Zn
(c) Na > Al > Zn > Mg
(d) Mg > Na > Al > Zn
Answer:
(b) Na > Mg > Al > Zn

Explanation: Almost all metals combine with oxygen to form metal oxide. However, the reactivities of different metals towards oxygen are different. The most reactive of the given metals is Na followed by Mg, Al and Zn.

(D) Which of the following metal oxides are soluble in water?
(I) CuO
(II) Na20
(III) FeO
(IV) K20
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) Both (II) and (IV)
(d) Both (I) and (IV)
Answer:
(c) Both (II) and (IV)

Explanation: Most metal oxides are
insoluble in water but some of these dissolve in water to form alkalis. Sodium oxide and potassium oxide dissolve in water to produce alkalis as follows:
Na₂O(s) + H₂O(l) → 2NaOH(aq)
K₂O(s) + H₂O(l) → 2KOH(aq)

(E) Metals such as sodium and potassium are kept immersed in:
(a) Kerosene oil
(b) Water
(c) Carbon disulphide
(d) Alcohol
Answer:

Question 9.
Pritha’s mother had lots of silver jewellery which she had kept in a jewellery box. One day, when she took them out to show them to her friends, she was surprised to see that most of them had a black coating over them.

Silver articles become black on prolonged exposure to air. This is due to the formation of:
(a) Ag₃N
(b) Ag₃O
(c) Ag₂S
(d) Ag₃S and Ag₃N
Answer:
(c) Ag₂S

Explanation: Silver metal reacts with atmos¬pheric sulphur compounds like H₂S gas and forms a black coating of Ag₂S over the surface. This reaction is as below:

Question 10.
Take samples of sodium chloride, potassium iodide, barium chloride or any other salt from the science laboratory. Take a small amount of a sample on a metal spatula and heat directly on the flame as shown in fig. Also try to dissolve the samples in water, petrol and kerosene.

Heating a sail sample on a spatula

Make a circuit as shown in Fig. and insert the electrodes into a solution of one salt.

(A) The physical state and properties of the salt samples used in the activity is:
(I) All are crystalline solids
(II) All are brittle
(III) Not all are hard
(IV) Not all are brittle
Which of the statements above is correct?
(a) Both (I) and (III)
(b) Both (I) and (II)
(c) Both (II) and (III)
(d) Both (III) and (IV)
Answer:
(b) Both (I) and (II)

Explanation: All the salts are ionic compounds and are crystalline solids and hard due to the strong force of attraction between the positive arid negative ions. They are also brittle.

(B) Select the correct, observation when the salt sample is taken on a metal spatula and heated directly on the flame:
(a) The salts melt immediately
(b) The salts give out characteristics flame upon heating
(c) The salts do not melt easily
(d) The salts undergo sublimation
Answer:
(c) The salts do not melt easily

Explanation: The given salts are ionic compounds that have very high melting and boiling points as a large amount of energy is required to break the strong inter-ionic attraction.

(C) The solution of which of the following compounds will not conduct electricity?
(a) CCl₄
(b) NaCl
(c) CaCl₂
(d) KBr
Answer:

(D) A student noted the following observations with four compounds A, B, C and D.

Which of the compounds A, B, C and D are ionic compounds?
(a) A and B
(b) B and C
(c) C and D
(d) A and D
Answer:

(E) Select the correct statement regarding the electrical conductivity of ionic compounds:
(a) The salt samples in the activity conduct electricity in their solid-state.
(b) The salt samples in the activity conduct electricity in a solution of water.
(c) The salt samples do not conduct electricity in a molten state.
(d) The salt samples do not conduct electricity in solution or in molten state.
Answer:

Question 11.
Displacement reactions are very important reactions of chemistry. They have many applications in various fields some of which are listed below:
(1) It is used in thermite welding.
(2) It is used in making alloy steel.
(3) It is used in the extraction of various metals.
(4) It is used in treating acid indigestion.
A thermite reaction is a single displacement reaction between iron oxide and aluminium which is also a highly exothermic reaction. The extreme heat released from this reaction is sufficient to melt the iron product.

(A) The correct chemical equation describing the thermite process is:
(a) Fe₂O₃(s) + 2Al(s) + Heat → 2Fe(s) + Al₂O₃(l)
(b) Fe₂O₃(s) + 2Al(S) → 2Fe(l) + Al₂O₃(s) + Heat
(c) 3FeO(s) + 2Al(S) + Heat → 3Fe(l) + Al₂O₃(s)
(d) 3FeO(s) + 2Ai(s) → 3Fe(l) + Al₂O₃(s) + Heat
Answer:
(b) Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat

Explanation: Thermite reaction is the reaction between iron (III) oxide or Fe₂O₃ and aluminium. It is a highly exothermic process (shown by “+ Heat” in the product side) and iron is produced in the molten state. It is used to join is used tojoin railway tracks or cracked machine parts.

(B) What happens when zinc metal is added to G test tube containing Al₂(SO₄)₃ solution?
(a) Zinc displaces aluminium from its salt solution
(b) No reaction takes place
(c) The solution becomes blue in colour
(d) The solution becomes colourless and aluminium metal is deposited.
Answer:
(b) No reaction takes place

Explanation: No reaction takes place as zinc is less reactive than aluminium and cannot displace aluminium from its salt solution, namely, Al₂(SO₄)₃ solution.

(C) A student made the following observations after studying the following displacement reactions between a metal and a salt solution of a different metal:
(i) Mg + ZnSO₄ → MgSO₄ + Zn
(ii) Zn + CuSO₄ → ZnSO₄ + Cu
(iii) Co + MgSO₄ → CaSO₄ + Mg
Selsect the incorrect observation(s):
(i) Calcium will displace copper from copper sulphate solution.
(II) Magnesium will be displaced by both calcium and zinc
(II) The least reactive metal out of Mg, Ca, Cu and Zn are Zinc.
(IV) The most reactive metal out of Mg, Ca, Cu and Zn is calcium.
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) Both (II) and (III)
(d) Both (I) and (IV)
Answer:

(D) An activity was performed by a student to find the reactivity of four metals- A, B, C and D by taking salt solutions of four metals in four test tubes numbered 1 to 4 and adding the samples of each metal one by one to each of the test tubes.

The observations recorded by the student are as given below:

The correct arrangement of the given metals A, B, C and D in decreasing order of their reactivities is:
(a) C < B < A < D
(b) B < C < A < D
(c) C < B < D < A
(d)D < A < B < C
Answer:

(E) A student performed an experiment to study the displacement reaction of metals. He took two test tubes X and Y containing copper sulphate and silver nitrate solutions respectively.

He dipped a strip of zinc in test tube X and copper strip in test tube Y and recorded his observations as shown below. Select the correct observation:

Answer:
(d) Test Tube X: Reaction takes place; Test Tube Y: Reaction takes place.

Explanation: Zinc is more reactive than copper and will displace copper from copper (II) sulphate solution in test tube X.
Zn + CuSO₄ → ZnSO₄ + Cu
Also, copper is more reactive than silver and will displace silver from silver nitrate solution in test tube Y.
Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag

Question 12.
A fusible metal alloy is used to create a permanent bond between metal workpieces. The alloy is melted in order to adhere to and connect the pieces after cooling, which requires that the alloy have a lower melting point than the pieces being joined. The alloy should also be resistant to oxidative and corrosive effects that would degrade the joint over time.

Name an alloy that is used for welding electrical wires together and also give its composition.
Answer:
Solder is an alloy that is used for welding electrical wires together. It is an alloy of lead and tin (Pb and Sn) and has a low melting point.

Question 13.
Sam went to the grocery store with his mother one day.
He observed that pickles, curds and other sour things are always stored in glass or plastic containers and never in any container made of a metal or alloy. He later found out that this is related to the chemical properties of metals as metals react with acids.

(A) Metals react with dilute acids to give:
(a) Salt and water
(b) Salt and hydrogen gas
(c) Salt and carbon dioxide gas
(d) Salt, water and carbon dioxide gas
Answer:
(b) Salt and hydrogen gas

Explanation: Most metals react with dilute acid to give the metal salt and hydrogen gas. Example:
Zn(s) + H₂SO₄ (aq) → ZnSO₄(aq)) + H₂(g)

(B) Which of the following metal will react with dilute hydrochloric acid?
(I) Cu
(II) Zn
(III) Al
(IV) Ag
(a) Only (I)
(b) Only (II)
(c) Both (I) and (IV)
(d) Both (II) and (III)
Answer:

(C) Which of the following oxides will not react with dilute sulphuric acid?
(a) CO₂
(b) CuO
(c) MgO
(d) Na₂O
Answer:

(D) Some students reacted an insoluble metal oxide with a dilute acid to form a soluble salt with a characteristic blue colour.
The insoluble metal oxide and the soluble salt could be:

Answer:

(E) The correct arrangement of metals Mg, Zn, Fe and Al in decreasing order of their reactivity with dilute acids is:
(a) Al > Mg > Zn > Fe
(b) Al > Mg > Fe > Zn
(c) Mg > Al > Zn > Fe
(d) Mg > Al > Fe > Zn
Answer:
(c) Mg > Al > Zn > Fe

Explanation: Out of the metals Mg, Zn, Fe and Al, Mg will react most vigorously with dilute acid, followed by Al, Zn and Fe.

Question 14.
While walking along the roadside with his grandfather, Aman observed that many iron pipes had developed cracks on their surfaces.

(A) Metals react with dilute acids to give:
(a) Salt and water
(b) Salt and hydrogen gas
(c) SaLt ared carbon dioxide gas
(d) Salt, water and carbon dioxide gas
Answer:
(b) Salt and hydrogen gas
Explanation: Most metals react with dilute acid to give the metal salt and hydrogen gas.
Example:
Zn(s) + H₂SO₄ (aq) → ZnSO₄(aq) + H₂(g)

(B) Which of the following metal will react with dilute hydrochloric acid?
(I)Cu
(II)Zn
(III)AL
(IV)Ag
(a) Only (I)
(b) Only (II)
(c) Both (I) and (IV)
(d) Both (il) and (III)
Answer:

(C) Which of the following oxides will not react with dilute sulphuric acid?
(a)CO₂
(b)CuO
(c) MgO
(d) Na₂O

(D) Some students reacted an insoluble metal oxide with a dilute acid to form a soluble salt with a characteristic blue colour.
The insoluble metal oxide and the soluble salt couLd be:

(E) The correct arrangement of metals Mg, Zn, Fe and AL in decreasing order of their reactivity with diLute acids is:
(a) Al > Mg > Zn> Fe
(b) Al > Mg> Fe > Zn
(c) Mg > Al> Zn > Fe
(d) Mg > Al > Fe > Zn
Answer:
(c)Mg > Al > Zn > Fe
Explanation: Out of the metals Mg, Zn, Fe and Al, Mg will react most vigorously with dilute acid, folLowed by At. Zn and Fe.

Question 15.
While walking along the roadside with his grandfather, Aman observed that many iron pipes had developed cracks on their surfaces.

Being inquisitive in nature and atso having Learned about the phenomenon of corrosion, Aman searched the internet for more information about corrosion and its prevention and found out that the most important factor in atmospheric corrosion, overriding pollution or lack of it, is moisture, either in the form of rain, dew, condensation, or high relative humidity (RH). In the absence of moisture, most contaminants would have little or no corrosive effect.

(A) Identify the correct statement:
(a) Rusting of iron is caused only by water.
(b) Rusting of iron is caused only by air,
(c) Rusting of iron is caused only by impurities.
(d) Rusting of iron is caused by both air and water.
Answer:

(B) Two students noted down the following observations after studying the graph showing the effect of reLative humidity on the rate of corrosion in iron


Select the correct option.
(C) Chemically rust is:
(a) Hydrated Iron (II) oxide
(b) Hydrated Iron (III) oxide
(c) Iron (III) sulphate
(d) Iron (III) oxide
Answer:
(c) Student A: Rate of corrosion is high for neiative humidity between 50% – 60%; Student B: Rate of corrosion… >60%.

Explanation: From the graph, we observe that the rate of corrosion depends upon the relative humidity and it increases with increase in the relative humidity.

Rate of corrosion is minimal for relative humidity < 40 %, is low for relative humidity between 40 % to 50 %. is high for relative humidity between 50% – 60 % and is extreme for relative humidity > 60 %.

(D) Which of the following statement is /are incorrect about corrosion?
(I) The black coating on silver articles is due to formation of basic silver oxide when silver reacts with oxygen present in air.
(II) The green coating on copper articles is due to formation of copper carbonate.
(III) The brown flaky substance formed on iron articles is due to the formation of rust.
(IV) The black coating on silver articles is due to formation of silver sulphide when silver reacts with hydrogen sulphide present in air.
(a) Only (I)
(b) Only (II)
(c) Both (I) and (III)
(d) Both (II) and (IV)
Answer:
(a) Only (I)

(E) 0 Rusting of iron can be prevented by :
(a) Galvanisation only
(b) Alloying only
(c) Both (a) and (b)
(d) Neither (a) nor (b)
Answer:

Very Short Answer Type Questions

Question 1.
A metal combines with a non-metal to form a compound Y. Will it dissolve in an organic solvent or not?
Answer:
Metals combine with non-metals to form ionic compounds by transfer of electrons. Ionic compounds do not dissolve in organic solvents but are soluble in water.

Question 2.
An element E combines with 02 to form an oxide E20, which is a good conductor of electricity. Write the formula of the compound formed when it combines with chlorine?
Answer:

Question 3.
Why do ionic compounds conduct electricity in molten state?
Answer:
ionic compounds conduct electricity in molten state because the ions move freely in molten state since the electrostatic force of attraction between oppositely charged ions is overcome due to heat.

Question 4.
Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Answer:
Usually, metal sulphides and carbonates are converted to metal oxides in the process of extraction of metal. This is because extraction of a metal from its oxide is easier as compared to its extraction from its sulphides and carbonates. Metal oxides can easily reduce to metal with the help of a common reducing agent like coke.

Question 5.
From amongst the metal, sodium, calcium, aluminium, copper and magnesium, name the metal:
(A) Which reacts with water only on boiling.
(B) Another one which does not. react even with steam.
Answer:
(A) The metal which reacts with water only on boiling is magnesium as it does not react with cold water.
(B) The metal which does not react even with steam is copper.

Question 6.
An element ‘A’ form two oxides AO and AO₂. The oxide AO is neutral whereas the oxide AO₂ is acidic in nature. Would you call element ‘A’ a metal or a non-metal?
Answer:

MCQ Questions for Class 10 Science with Answers

Class 10 Science Chemistry MCQ:

• Chemical Reactions and Equations Class 10 MCQ
• Acids, Bases and Salts Class 10 MCQ
• Metals and Non-metals Class 10 MCQ
• Carbon and Its Compounds Class 10 MCQ
• Periodic Classification of Elements Class 10 MCQ

Class 10 Science Chemistry Chapter 5 MCQ With Answers

Chemistry Class 10 Chapter 5 MCQs On Periodic Classification of Elements

Periodic Classification Of Elements Class 10 MCQ Question 1.
Which of the following statements) about the modern periodic table are incorrect?
(I) The elements in the modern periodic table are arranged on the basis of their decreasing atomic numbers.
(II) The elements in the modern periodic table are arranged on the basis of their increasing atomic masses.
(III) Isotopes are placed in adjoining group(s) in the periodic table.
(IV) The elements in the modern periodic table are arranged on the basis of their increasing atomic number.
(a) Only (I)
(b) (I), (II), and (III)
(c) (I), (II), and (IV)
(d) Only (IV)
Answer:
(b) (I), (II), and (III)

Explanation: The modern periodic table is a tabular arrangement of elements in increasing order of their atomic number, which is why isotopes are placed at the same position. Hence, only (III) is correct.

Periodic Table Class 10 Icse MCQ Question 2.
Which of the following statements about the modern periodic table is correct?
(a) It has 18 horizontal rows known as periods.
(b) It has 7 vertical columns rows known as periods.
(c) It has 18 vertical columns known as groups.
(d) It has 7 horizontal rows known as groups.
Answer:

MCQ On Periodic Classification Of Elements Question 3.
An element X is forming the acidic oxide. Its most probable position in the modern periodic table is:
(a) Group 1 and Period 3
(b) Group 16 and Period 3
(c) Group 17 and Period 3
(d) Group 2 and Period 3
Answer:

Class 10 Science Chapter 5 MCQ Question 4.
Which of the given elements A, B, C, D and E with atomic numbers 2, 3, 7,10 and 30 respectively belong to the same period?
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E
Answer:

MCQ On Periodic Classification Of Elements Class 10 Pdf With Answers Question 5.
On the basis of the electronic configuration of x|, the group number and period of the element ‘X is:
(a) Group 15 period 2
(b) Group 13 period 2
(c) Group 9 period 5
(d) Group 13 period 5
Answer:
(b) Group 13 period 2

Explanation: From X⁹₅, we can have the information as:
X — element
5 — Atomic number
9 — Mass number
The electronic configuration of X is 2, 3.

Group number is found out on the basis of valance electrons. Valence electrons are 3 so group number is 10 + 3 = 13.

The period can be found out by knowing the number of shells. Since the number of shells is 2 so it belongs to period 2.

Valence Electron Calculator – This free calculator provides you with free information about Valence Electron.

Periodic Classification Of Elements MCQ Question 6.
The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively.
Which pair of elements belongs to the same group?
(a) A and B
(b) B and D
(c) A and C
(d) D and E
Answer:

MCQ Of Periodic Classification Of Elements Question 7.
An element ‘X‘ with atomic number 11 forms a compound with element ‘V with atomic number 8. The formula of the compound formed is:
(a) XY
(b) X₂Y
(c) XY₂
(d) X₂Y₃
Answer:
(b) X₂Y

Element X can lose one electron and has a configuration like that of Neon.
X → X⁺ + e^–
Element Y can gain two electrons to acquire noble gas configuration like that of Neon:
Y + 2e^– → Y₂^–
Or we can write

Periodic Table MCQ Questions And Answers Question 8.
The positions of four elements A, B, C, and D in the modern periodic table are shown below.

Which element is most likely to form an acidic oxide?
(a) A
(b) B
(c) C
(d) D
Answer:

Chapter 5 Science Class 10 MCQ Question 9.
In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which of the following element found a place in the periodic table later?
(a) Germanium
(b) Chlorine
(c) Oxygen
(d) Silicon
Answer:

Class 10 Science Ch 5 MCQ Question 10.
Elements P, Q, R, and S have atomic numbers 11,15,17 and 18 respectively. Which of them are reactive non-metals?
(a) P and Q
(b) P and R
(c) Q and R
(d) R and S
Answer:
(c) Q and R

Chapter 5 Class 10 Science MCQ Question 11.
An element which is an essential constituent of all organic compounds belongs to:
(a) Group 1
(b) Group 14
(c) Group 15
(d) Group 16
Answer:

MCQs Of Periodic Classification Of Elements Question 12.
According to Mendeleev’s periodic law, the elements were arranged in the periodic table in the order of:
(a) Increasing atomic number
(b) Decreasing atomic number
(c) Increasing atomic masses
(d) Decreasing atomic masses
Answer:
(c) Increasing atomic masses

Explanation: Mendeleev’s periodic law is an arrangement of elements in increasing order of their atomic masses as Mendeleev’s periodic law states that, the physical and chemical properties of elements are a periodic function of their atomic masses.

Class 10 Chapter 5 Science MCQ Question 13.
Which of the following is the outermost shell for elements of period 2?
(a) K shell
(b) L shell
(c) M shell
(d) N shell
Answer:

MCQ Periodic Classification Of Elements Question 14.
Which of the following gives the correct increasing order of the atomic radii of O, F, and N?
(a) O, F, N
(b) N, F, O
(c) O, N, F
(d) F, O, N
Answer:

Periodic Table Class 10 MCQ Question 15.
Arrange the following elements in the order of their decreasing metallic character Na, Si, Cl, Mg, Al:
(a) Cl > Si > Al > Mg > Na
(b) Na > Mg > Al > Si > Cl
(c) Na > Al > Mg > Cl > Si
(d) Al > Na > Si > Ca > Mg
Answer:

Question 16.
Which among the following elements has the largest atomic radii?
(a) Na
(b) Mg
(c) K
(d) Ca
Answer:
(c) K

Explanation: Na and Mg belong to the same period, whereas Na and K are in the same group. In a group from top to bottom, the atomic radius increases, whereas it decreases in a period from left to right. Hence, the order would be K > Na > Mg and K > Ca > Mg.

Related Theory:
Atomic radius represents the distance from the nucleus to the outer shell of an element.
The trend of the atomic radius in the periodic table:

1. decreases going from left to right of a period
2. increases going down a group.

Question 17.
The electronic configurations of three elements X, Y and Z are:
X : 2 Y: 2, 8, 7 Z : 2, 8, 2
Which of the following is correct regarding these elements?
(a) X is a metal
(b) Y is a metal
(c) Z is a non-metal
(d) Y is a non-metal and Z is a metal
Answer:
(d) Y is a non-metal and Z is a metal.

Explanation: Element Y has 1 less electron to complete its octet which is a property of non-metals. On the other hand, element Z has 2 extra electrons to become stable which is a property of metals..

Question 18.
Which of the following elements would lose an electron easily?
(a) Mg
(b) Na
(c) K
(d) Ca
Answer:

Question 19.
Which of the following elements does not lose an electron easily?
(a) Na
(b) F
(c) Mg
(d) Al
Answer:
(b) F

Explanation: Flourine has 7 electrons in the outermost orbit. Its atom size is the smallest too. Since it is the most electronegative element, it does not lose an electron easily. Sodium has one valence electron, magnesium has 2 valence electrons, and aluminium has 3 valence electrons. All these metals lose electrons easily.

Related Theory
Metals can easily lose electrons and exhibit electropositive nature, whereas non-metals have a tendency to accept electrons and exhibit electronegative nature. Na, Al, and Mg are metals, whereas F is non-metal.

Question 20.
What type of oxide would Eka-aluminium form?
(a) EO₃
(b) E₃O₂
(c) E₂O₃
(d) EO
Answer:

Question 21.
The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?
(a) Metal
(b) Metalloid
(c) Non-metal
(d) Left-hand side element
Answer:
(b) Metalloid

Explanation: Atomic number 14 (electronic configuration of 2,8,4) is for silicon element, which is a metalloid and exhibits properties of both metal and non-metal. It has 4 electrons in its valence shell, so it tends to form covalent acidic oxide.

Question 22.
Which one of the following depicts the correct representation of atomic radius (r) of an atom?

(a) (I) and (II)
(b) (II) and (III)
(c) (III) and (IV)
(d) (I) and (IV)
Answer:
(b) (II) and (III)

Explanation: The distance between the center of the nucleus and the outermost shell is known as atomic radius.

Question 23.
Which one of the following does not increase while moving down the group of the periodic table?
(a) Atomic radius
(b) Metallic character
(c) Valence
(d) Number of shells in an element
Answer:

Question 24.
On moving from left to right in a period in the periodic table, the size of the atom:
(a) increases
(b) decreases
(c) does not change appreciably
(d) first decreases and then increases
Answer:
(b) decreases

Explanation: As we move from left to right in the period of periodic table, the number of shell remains same but atomic number increases. So, the increase in nuclear charge which tends to pull electrons closer to the nuclers and reduces the size of the atoms.

Related Theory
The size of atom of an inert gas is bigger than that of the preceding halogen atom. The greater size of the inert gas atom in a period is due to the structural stability of its outermost shell consisting of an octet of electrons.

Question 25.
Which of the following set of elements is written in order of their increasing metallic character?
(a) Be, Mg, Ca
(b) Na, Li, K
(c) Mg, Al, Si
(d) C, O, N
Answer:
(a) Be, Mg, Ca.

Explanation: As we move down in a group, the metallic nature of elements increases. Be, Mg, and Ca are present in the same group (group 2 of the modern periodic table). Thus, Ca has the highest metallic character.

Question 26.
An element X makes an oxide with the formula X₂O₃. This element will be in the same group as:
(a) Na
(b) Mg
(c) Al
(d) Cl [Diksha]
Answer:
(c) Al

Explanation: The answer is Al (aluminium). The element Al is in group II! of Mendeleev’s periodic table, in which the general formula of the oxides of elements is X₂O₃.

Question 27.
The two pairs of elements placed by Newlands in one slot are:
(a) Co, Ni and Ce, La
(b) Be, Mg and Co, Ni
(c) F, Cl, and Ce, La
(d) Zn, Sr, and Be, Mg
Answer:

Question 28.
The order of metallic character of some elements is: N < P < As < Sb < Bi. Identify the most electronegative among these elements,
(a) N
(b) P
(c) Sb
(d) Bi
Answer:
(a) N

Explanation: The less metallic an element, the more electro-negative it will be. Since electronegativity is the ability of an atom to gain electrons, whereas metallic character is related to the ability of atoms to lose electrons. As N is the least metallic of the given elements, it will be the most electronegative.

Question 29.
Four elements P, Q, R and S have number of valence electrons 2,3,5 and 7 respectively. A student noted down the Group number in Modern Periodic Table and their valency as:

Select the row containing the correct group number and valency.
Answer:

Question 30.
Consider the elements Li, Be, B, C, N, O and F.
(I) The most electropositive element is F.
(II) The most electronegative element is F.
(III) The only metalloid is B.
(IV) The smallest atomic size is Li.
Read the statements given above and select the incorrect statements:
(a) Both (I) and (III)
(b) Both (I) and (IV)
(c) Both (II) and (III)
(d) Both (II) and (IV)
Answer:
(b) Both (I) and (IV)

Explanation: Let us arrange the given elements according to their atomic number:
Li < Be < B < C < N < 0 < F.

All the above elements have two occupied shells and are therefore placed in the second group of the periodic table.

The most electropositive element is Li and the most electronegative element is F. This is because the tendency to lose electrons decreases as we go from left to right along a period. Also, as we go from left to right along a period, the atomic radius and hence the atomic size decreases because of the increase in effective nuclear charge experienced by the valence electrons. The only metalloid is B.

Question 31.
Out of the elements F, Cl, Br and I, which is the most electronegative element?
(a) F
(b) Cl
(c) Br
(d) I
Answer:
(a) F

Explanation: The electronegativity decreases as we move down a group because the ability to gain electrons decreases down a group. This is because of the decrease in the effective nuclear charge experienced by the valence electrons since a new shell is added in each group.

Since F, Cl, Br and I have 2, 3, 4 and 5 shells respectively, F is the most electronegative of these elements.

Assertion Reasoning questions Class 10 Science Chapter 5

For the following questions, two statements are given-one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true but (R) is not the correct explanation of the assertion.
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

Question 32.
Assertion (A): Potassium has a bigger atomic radius than lithium.
Reason (R): Atomic radius decreases along a period.
Answer:

Question 33.
Assertion (A): Chemical properties of the elements belonging to the same group are the same.
Reason (R): Elements belonging to the same group possess the same number of valence electrons.
Answer:
(a) Both (A) and (R) are true and (R) is the correct explanation of A.

Question 34.
Assertion (A): Nitrogen is a non-metal.
Reason (R): Nitrogen has 5 valence electrons.
Answer:
(a) Both (A) and (R) are true and (R) is the correct explanation of (A)

Explanation: Non-metals are the elements that form negative ions by gaining electrons.

Electronic configuration of N = 2 5
k = 2
L = 5
It needs 3 electrons to complete its octet and achieve the same configuration as that of the inert gas neon.
N + 3e^– → N^3-

Question 35.
Assertion (A): Newland’s law of Octaves worked well with lighter elements only.
Reason (R): Newland assumed that only 56 elements existed in nature.
Answer:

Question 36.
Assertion (A): A correct position could not be assigned to hydrogen in Mendeleev’s periodic table.
Reason (R): Mendeleev Periodic Law states that ‘the properties of elements are the periodic function of their atomic numbers.
Answer:
(c) (A) is true but (R) is false

Explanation: A correct position could not be assigned to hydrogen in the periodic table. The electronic configuration of hydrogen resembles that of alkali metals. Like alkali metals, hydrogen combines with halogens, oxygen and sulfur to form compounds having similar formulae.

On the other hand, just like halogens, hydrogen also exists as diatomic molecules and it combines with metals and non-metals to form covalent compounds.

Moreover, Mendeleev’s Periodic Law states that ‘the properties of elements are the periodic function of their atomic masses’.

Question 37.
Assertion (A): The elements Sodium (Na), Magnesium (Mg), Aluminium (Al) belong to the same group in Modern Periodic Table.
Reason (R): Atoms of different elements with the same number of occupied shells are placed in the same period.
Answer:

Question 38.
Assertion (A): Calcium (Atomic No. 20) is more metallic than Potassium (Atomic No. 19).
Reason (R): The tendency to lose electrons decreases as we move from left to right in a period.
Answer:
(c) (A) is false but (R) is true.

Explanation: Potassium (Atomic No. 19) is more metallic than Calcium (Atomic No. 20) as the tendency to lose electrons decreases as we move from left to right in a period.

The electronic configuration of Potassium is 2, 8, 8, 1 and that of Calcium is 2, 8, 8, 2. Therefore, the effective nuclear charge acting on the valence electrons of Calcium will be more than that of Potassium.

(Competency Based Questions (CBQs))

Question 1.
Sulphur is a multivalent non-metal, abundant, tasteless and and odorless. In its native form sulphur is a yellow crystalline solid. In nature it occurs as the pure element or as sulphide and sulphate minerals.Sulphur dioxide or sulphur dioxide is the chemical compound with the

formula SO₂. It is a toxic gas responsible for the smell of burnt matches. It is released naturally by volcanic activity and is produced as a by product of copper extraction and the burning of fossil fuels contaminated with sulphur compounds.
Identify the group and period of the Modern Periodic Table to which Sulphur belongs. Write any two properties exhibited by sulphur.
Answer:
The atomic number of sulphur is 16. It’s electronic configuration is (2, 8, 6). It belongs to group 16 and period 3 of the Modern Periodic Table.

Two properties exhibited by sulphur are allotropy and catenation.

Question 2.
Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.

The main credit for classifying elements goes to Mendeleev for his most important contribution to the early development of a Periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The formulae of their hydrides and oxides were treated as basic criteria for the classification of the elements. However, Mendeleev’s classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.
(A) State Mendeleev’s Periodic Law.
Answer:
Mendeleev’s Periodic Law: It states that the properties of elements are the periodic function of their atomic masses.

Related Theory
Mendeleev concluded that when elements are arranged in order of increasing atomic masses, similar properties of element repented after a definite gap of atomic masses. This repetition of similar properties after a definite gap of atomic masses is also called periodicity in properties.

(B) Why did Mendeleev leave some gaps in the Periodic table?
Answer:

(C) If the letter ‘R‘ was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as:
(a) RH₄, RO
(b) RH₄, RO₂
(c) RH₂, RO₂
(d) RH₂, RO
Answer:

(D) Isotopes are:
(a) Atoms of an element with similar chemical properties but different atomic masses.
(b) Atoms of different elements with similar chemical properties but different atomic masses.
(c) Atoms of an element with different chemical properties but same atomic masses.
(d) Atoms of different elements with different chemical properties but same atomic masses.
Answer:
(a) Atoms of an element with similar chemical properties but different atomic masses.

Explanation: Isotopes are the atoms of some element which have same atomic number but different mass number. They have same atomic number, same number of protons, same number of electrons and, same number of valence electrons. Valence electrons are responsible for the chemical properties of an element. Since isotopes of an element have same number of valence electrons. So they will have similar chemical properties.

Related Theory
Isotopes of chlorine are Cl-35 and Cl-37:

Hence, isotopes of chlorine Cl-35 and Cl-37 will have similar chemical properties.

Question 3.
Recently, two persons died in a major ammonia gas leakage at the Indian Farmers Fertilizer Cooperative Limited (IFFCO) unit at Prayagraj. The experts point out that ammonia is stored for industrial use in liquid form under high pressure or in gaseous form at low temperature, as was the case in the IFFCO unit where the accident took place. Ammonia is critical in the manufacturing of fertilizers, and is one of the largest-volume synthetic chemicals produced in the world.

What type of bond is present ammonia molecule? Wilt a solution of ammonia be a good conductor or poor conductor of electricity?
Answer:
Ammonia molecule NH3 is formed by the sharing of electrons between nitrogen and hydrogen atoms as shown below:

As electron pairs are shared between the three hydrogen atoms and the nitrogen atom, a solution of ammonia in water will be a poor conductor of electricity as there are no charged particles present in an ammonia molecule.

Question 4.
The following table shows a part of the periodic table in which the elements are arranged according to their atomic numbers. (The letters given here are not the chemical symbols of the elements):

(A) Which element has a bigger atom, a or f?
Answer:
a (size decreases from left to right in a period).

(B) Which element has a higher valency, k or o?
Answer:

(C) Which element is more metallic, i or k?
Answer:
i (metallic character decreases from left to right in a period).

Explanation:

it has to lose only one electron to acquire metallic character whereas k has to lose 3 electrons which requires a lot of energy as compared to element so element i is more metallic.

(D) Select a letter which represents a non-metal of valency 2.
Answer:

Question 5.
When Sam was walking along the street, he saw several beautiful and colourful signages. In the signage industry, neon signs are electric signs lighted by long luminous gas-discharge tubes that contain rarefied neon or other gases. They are the most common use for neon lighting, which was first demonstrated in a modern form in December 1910 by Georges Claude at the Paris Motor Show.

Where would you locate the element with electronic configuration 2, 8 in the modern periodic table?
(a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10
Answer:
(c) Group 18
Explanation: The element with electronic configuration 2, 8 has an octet configuration, so it must be an inert gas, i.e., neon, which is placed in group 18.

Related Theory
Group 18 in the modern periodic table has noble gases (inert gases). Helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn) are present in group 18. The members of the group have eight electrons in their outermost orbit (except helium which has two electrons). Thus, they have a stable electronic configuration. These gases are chemically un-reactive, i.e., they don’t react with other elements to form compounds.

Question 6.
Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electron shells but different number of electrons in their outermost shells. It was found that elements A and G combine to form an ionic compound. This ionic compound is added in a small amount to almost all vegetables and dishes during cooking. Oxides of elements A and B are basic in nature while those of elements E and F are acidic. The oxide of element D is, however, almost neutral.
Based on the above information, answer the following questions:
(A) To which group or period of the periodic table do these elements belong?
Answer:

(B) What would be the nature of compound formed by a combination of elements B and F?
Answer:
The compound between B and F will be ionic in nature.

(C) Which two of these elements could definitely be metals and which would be non metals?
Answer:

(D) Which one of the eight elements is most likely to be found in gaseous state at room temperature?
Answer:
Element H will be found in gaseous state at room temperature as it is the 8th element of the group so it would have 8 electrons in its outermost shell which is the electronic configuration of a nobel gas.

Related Theory:
Sodium chloride is used in almost all vegetables and dishes during cooking. It means A is sodium and G is chlorine.
Metals are one present on the left hand side of modern periodic table and non-metals on the right hand side. As we know oxides of metals are basic in nature and oxides of non-metals form acidic oxide. The elements given one.

Question 7.
Analyse the following table given below and answer the questions that follow:
Given alongside is a part of the periodic table. As we move vertically downward from Li to Fr:

(A) Which among the following has larger size of atoms?
(a) Li
(b) Na
(c) Cs
(d) Fr
Answer:
(d) Fr

Explanation: Fr has greater atomic size as the atomic size increases gradually from lithium to francium.

(B) Which one of the following does not increase while moving down in group of the periodic table?
(a) Atomic radius
(b) Metallic character
(c) Valence
(d) Number of shells in an element
Answer:

(C) Name two properties of elements whose magnitude change while going from top to bottom in a group of the periodic table. In what manner do they change?
Answer:

(D) Rewrite the following statement after correction, if necessary:
“Groups have elements with consecutive atomic numbers”
Answer:
Periods have elements with consecutive atomic numbers.

Question 8.
In addition to its applications in electronic devices, germanium is used as a component of alloys and in phosphors for fluorescent lamps. Because germanium is transparent to infrared radiation, it is employed in equipment used for detecting and measuring such radiation, such as windows and lenses. Silicon is used in building and construction, able to bond materials such as concrete, glass, granite, steel and plastics, enabling them to work better and last longer. Solar cells made out of silicon currently provide a combination of high effciency, low cost, and long lifetime.

Three elements B, Si and Ge are:
(a) Metals
(b) Non-metals
(c) Metalloids
(d) Metal, non-metal and metalloid respectively
Answer:
(c) Metalloids

Explanation: The elements boron (B), silicon (Si) and germanium (Ge) exhibit intermediate properties of metals and non-metals, therefore, they are called as metalloids. These elements are placed in between metals and non-metals diagonally as a zigzag line to separate them.

Related Theory
A few other elements are arsenic (As), antimony (Sb), tellurium (Te), polonium (Po) and astatine (At).

Question 9.
Analyse the following table given below and answer the questions that follow:
The atomic radii of the element of the second period are given below:

(A) Arrange these elements in decreasing order of their atomic radii.
Answer:
Elements in decreasing order of their atomic radii

(B) Why does atomic radius decreases as we move from left to right in a period?
Answer:

(C) Which is not true about the noble gases?
(a) They are non-metallic in nature
(b) They exist in atomic form
(c) They are radioactive in nature
(d) Xenon is the most reactive among these
Answer:
(c) They are radioactive in nature.
Explanation: Noble gases are inert and are not radioactive in nature.

Related Theory
Noble gases cannot lose or gain or shore electrons as their outermost shell is complete.
He has 2 electrons in its K shell, which is completely filled as K shell can accommodate maximum of 2 electrons whereas Ne has 8 electrons in its L shell and its octet is complete so they exist in atomic form.

(D) Which of the following is the outermost shell for elements of period 2?
(a) K shell
(b) L shell
(c) M shell
(d) N shell
Answer:

Question 10.
A student tried to assign a correct position to hydrogen in Mendeleev’s Periodic Table by looking at its resemblance to alkali metals and the halogen family.
Another student wondered where she would place the isotopes of chlorine, Cl-35 and Cl-37 as they were atoms of the same element.

(A) No fixed position could be given to hydrogen in the Mendeleev’s Periodic Table as:
(I) Electronic configuration of hydrogen resembles that of alkali metals.
(II) Hydrogen combines with metals and non-metals to form ionic compounds.
(III) Hydrogen exists as diatomic molecules just like alkali metals.
(IV) Hydrogen combines with halogens, oxygen and sulphur to form compounds having similar formulae as alkali metals.
(a) Both (I) and (II)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (III) and (IV)
Answer:
(c) Both (I) and (IV)

Explanation: As Mendeleev’s periodic table was based on atomic mass, no fixed position could be assigned to hydrogen. However, it has one valence electron just like alkali metals Li, Na, K etc. Moreover, hydrogen combines with haLogens, oxygen and sulphur just like alkali metals do. However, hydrogen combines with metals and non-metals to form covalent bonds by sharing of electrons and exists as diatomic molecules like halogens.

(B) The formula of hydrides of elements belonging to a Group of Mendeelev’s Periodic Table is RH2. The Group Number to which the element belongs is:
(a) Group IV
(b) Group V
(c) Group VI
(d) Group VII

(C) The formula of oxides and hydrides of elements belonging to different Groups of the Mendeleev’s Periodic Table is given below:

The letter ‘R’ is used to represent any of the elements in the group.
Select the row containing incorrect information.
Answer:
(a) Croup No.: 1, Formula of oxides; RO, Formula of Hydrides; RH Explanation: The formula of hydrides and oxides of elements belonging to group I of Mendeleev’s table is R₂O and RH respectively. For example, formula of oxide and hydride of element Li will be Li₂O and LiH respectively.

(D) Select the correct statement regarding position of isotopes in Mendeleev’s Periodic Table:
(a) Mendeleev left some gaps in his periodic table for the isotopes.
(b) Isotopes were discovered after Mendeleev had proposed his periodic classification of elements.
(c) Mendeleev placed both the isotopes of chlorine (Cl-35 and Cl-37) under the same slot as they had same chemical properties.
(d) Mendeleev placed both the isotopes of chlorine (Cl-35 and Cl-37) in different slots as they had different masses.

(E) Mendeleev left some gaps in his Periodic Table as he predicted the existence of some elements that had not been discovered at that time. Which of the following elements discovered later, have properties similar to Eka-boron?
(a) Gallium
(b) Germanium
(c) Caesium
(d) Scandium
Answer:

Question 11.
We all have heard about the damage being done to the Taj Mahal and our environment due to high levels of oxides of certain elements in the atmosphere. Acid rain is caused by a chemical reaction that begins when these oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

Which of the following elements will form an acidic oxide?
(a) An element with atomic number 7
(b) An element with atomic number 3
(c) An element with atomic number 12
(d) An element with atomic number 19
Answer:
(a) An element with atomic number 7

Explanation: Non-metals form acidic oxides. The element with atomic number 7 is a non-metal (nitrogen). Rest three elements with atomic numbers, 3 (Li), 12 (Mg) andl9 (K) are metals and hence, form basic oxides.

Question 12.
Atomic radii of the elements of the second period are given below:
Period II elements: B Be O N Li C
Atomic radius (pm): 88 111 66 74 152 77
Atomic radii of first group elements are given below and arrange them in an increasing order.
Group 1 Elements 6: Na Li Rb Cs K
Atomic Radius (pm): 186 152 244 262 231
(A) Select the incorrect statements:
(I) The atomic radius decreases in moving from left to right along a period.
(II) The atomic radius increases in moving from left to right along a period
(III) As we move from left to right along a period, there is an increase in nuclear charge which tends to pull the electrons closer to the nucleus.
(IV) As we move from left to right along a period, there is a decrease in nuclear charge which tends to pull the electrons away from the nucleus.
(a) Both (I) and (III)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (II) and (IV)
Answer:
(d) Both (II) and (IV)

Explanation: As we move from left to right along a period we see that the atomic radius decreases. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.

(B) Two students recorded their observations on variation of atomic radii of first group elements as given below:

Select the row containing the correct observation by both students.
Answer:
(c) First student: Cs has the biggest atomic radius, Second student: Li has the smallest atomic radius.

Explanation: The atomic radius and hence the atomic size increases as we move down a group. This is because a new shell is added as we move down the group. This increases the distance between the nucleus and the valence shell.

As Cs lies at the bottom of group 1, and Li lies at the top, Cs has the biggest atomic radius among Group 1 elements.

(C) The atomic size of Na is greater than Li because:
(a) Na has three shells, whereas Li has two shells in its atom
(b) The atomic number of Na is greater than Li
(c) As we go down a group, distance between outermost electrons and nucleus decreases.
(d) The mass of Na atom is greater than Li atom
Answer:

(D) The graph of variation of atomic radius with atomic number for alkali metals and halogens is shown below:

Select the correct observation:
(a) Na has a bigger atomic radius than Li due to decrease in nuclear charge
(b) F has a smaller atomic radius than Li due to increase in nuclear charge
(c) Na and Cl belong to the third period of Modern Periodic Table and have identical electronic configuration.
(d) Elements of Group 17 have the biggest atomic size in their respective periods.
Answer:
(b) F has a smaller atomic radius than Li due to increase in nuclear charge

Explanation: Both F and Li lie in the second period as they have two occupied shells. However, as the effective nuclear charge is more in the case of F as compared to Li, F has a smaller atomic radius than Li.

The atomic radius decreases in moving from left to right along a period and it increases in going from top to bottom along a group.

(E) The correct increasing order of the atomic radii of the elements Mg, Si and Cl is:
(a) Mg > Si > Cl
(b) Si < Cl < Mg
(c) Cl < Si < Mg
(d) Cl < Mg < Si
Answer:

Question 13.
Chemists have always looked for ways of arranging the elements to reflect the similarities between their properties. The earliest attempt to classify the elements was in 1789, when Antoine Lavoisier grouped the elements based on their properties into gases, non-metals, metals and earths. Several other attempts were made to group elements together over the coming decades. In 1829, Johann Dobereiner recognised triads of elements with chemically similar properties, such as lithium, sodium and potassium, and showed that the properties of the middle element could be predicted from the properties of the other two. It was not until a more accurate list of the atomic mass of the elements became available at a conference in Karlsruhe, Germany in 1860 that real progress was made towards the discovery of the modern periodic table.
(A) Which of the following elements form Dobereiner’s triads?
(a) Li, Na, K
(b) Ca, Sr, Ba
(c) F, Cl, Br
(d) Cl, Br, I
Answer:

(B) Given below are four statements on Dobereiner’s triads:
(I) One triad identified by Dobereiner was (Ca, Na, Ba)
(II) The triads identified by Dobereiner had three elements each.
(III) The atomic mass of the middle element was roughly equal to the atomic masses of the other two elements.
(IV) Dobereiner could identify only three triads from the elements known at that time.
Identify the incorrect statements.
(a) Both (I) and (III)
(b) Both (II) and (III)
(c) Both (I) and (IV)
(d) Both (II) and (IV)
Answer:
(a) Both (I) and (III)

Explanation: Dobereiner’s triods consisted of three elements having simiLar properties. He coutd identifij onLy three triads out of the elements discovered at that time. They were (Li, Na, K), (Ca. Sr. Ba) and (Cl, Br, I). The atomic mass of the middle element was roughly equal to the average of the atomic masses of the other two elements.

(C) A & B are two elements having similar properties which obey the law of octaves. How many elements are there in between A and B?
(a) 5
(b) 6
(c) 7
(d) 8

(D) Which of the following is not a limitation of Newland’s law of octaves:
(a) The elements fluorine, chlorine and bromine are placed in the same column (musical note).
(b) Newlands’ Law of Octaves worked well with lighter elements only.
(c) Newlands assumed that only 56 elements existed in nature and no more elements would be discovered in the future.
(d) In order to fit elements into his Table, Newlands adjusted cobalt and nickel in the same slot.
Answer:
(a) The elements fluorine, chlorine and bromine are placed in the same column (musical note).

Explanation: The elements fluorine, chlorine and bromine are placed in the some column (musicol note) as they have similar properties and are known as halogens. Even in the modern periodic table, they are placed in the same group, group 17.

(E)Given below are few observations on properties of eLements.

Select the option containing the correct observation.
Answer:
(d) Observation: Properties of Li and Na were found to be similar, Doberimer’s Triods: Yes, NewLands’ Law Yes.

Explanation: Both Be and Mg were placed under the same note in Newland’s law, but were not part of Döbereiner’s triads. Dobereiners Triads

Question 14.
Valency of an element is the combining capacity of an atom of the element. The volency of an element is related to how many electrons are in the outer shell. The chemical formula for a substance shows how many atoms of each element are present in a molecule, or the proportion of atoms of each element. The formula can be worked out using the volency.

The molecular formula of a compound can be predicted knowing the valency of the constituting atoms. Knowledge of valency is useful in calculating equivalent weight of elements, writing down chemical equations and in checking the structures of molecules. Some elements show variable valency and the valency determines the properties of elements. The table below gives atomic number of five elements written as P, Q, R, S and T, which are not their real chemical symbols.

(A) The valency and group number in Modern Periodic Table of four elements are given below:

Select the option containing the correct valency and group number.
Answer:

(B) The electronic configuration of the element T is:

(C) The valency of elements:
(a) Decreases as we go down a group
(b) Remons same in a group
(c) Increases as we go down a group
(d) First increases and then decreases as we go down a group
Answer:
(b) Remains same in a group

Explanation: The valency of elements is equal to the number of valence electrons in case of metals and (8 – valence electrons) for non-metals. Moreover, all elements belonging to the same group have same outer shell electronic configuration. Therefore, valency of elements remains same in a group.

(D) As per the table given above, the element(s) which wilL form only covaLent bonds ¡s:
(I) P
(II) R
(III) S
(IV) Q
(a) Only (I)
(b) Only (II)
(c) Both (I) and (IV)
(d) Both (II) and (III)
Answer:

(E) Select the incorrect statement:
(a) Valency of elements of second period is 2.
(b) Valency of an element is determined by the number of valence electrons present in the outermost shell of its atom.
(c) Valency of metals is equal to the number of valence electrons.
(d) Valency of elements of Group 18 of Modern Periodic Table is 0.
Answer:

Question 15.
The elements can be classified as metals, nonmetals, or metalloids. In the Modern Periodic Table, a zig-zag line separates metals from non-metals.

The metals are to the Left of the line (except for hydrogen, which is a nonmetaL), the nonmetals are to the right of the Line, and the elements immediately adjacent to the line are the metalioids.
Ionization energy is the minimum amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule. It is expressed as
X(g) + energy → X⁺(g) + e^–

where X is any atom or molecule, X+ is the ion with one electron removed, and e- is the removed electron.
Since the metals are further to the left on the periodic table, they have low ionization energies.
(A) Which of the following elements is not a metalloid?
(a) Si
(b) Ge
(c) As
(d) Ar
Answer:
(d)Ar

Explanation: The metalloids are B, Si. Ge, As, Te and Po. Ar (Argon) is a noble gas having atomic number 18.

(B) An element A (atomic number 17) reacts with an element B (atomic number 14) to form a tetravalent halide.
Select the option which gives the correct nature of elements A and B:

Answer:

(C) Four statements are given below.
(I) The metalloids are placed in Groups 13 – 16 in the Modern Periodic Table
(II) Boron is the only metalloid in group 13 of the Modern Periodic Table.
(III) Group 14 of the Modern Periodic Table contains only metalloids.
(IV) Group 17 of the Modern Periodic Table contains both metalloids and non-metals
Select the correct statement(s):
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) Both (II) and (IV)
(d) (I), (II) and (IV)
Answer:

(D) Variation of the ionization energy of elements with atomic number upto atomic number 20 is given below:
From the graph we can conclude that the tendency to lose electrons:
(a) Increases as we go down the group
(b) Decreases as we go down the group
(c) Remains constant in a group
(d) No definite conclusion can be made
Answer:

(E) The metalloid which is the second most abundant element on earth’s crust after oxygen and is widely used in electronics is:
(a) B (b) Ge
(c) Si (d) As
Answer:

Very Short Answer Type Questions

Question 1.
State the common characteristic of the following elements: Boron, Silicon, Germanium and Arsenic
Answer:

Question 2.
State the Periodic Law on which the Modern Periodic Table is based.
Answer:
Periodic Law on which the Modern Periodic Table is based is termed as Modern Periodic Law. According to Modern Periodic Law – The properties of elements are a periodic function of their atomic numbers.

Related Theory
Modern Periodic Table or Long form of Periodic table was prepared by Henry Moseley and is based on electronic configuration of elements. The elements are arranged in increasing order of their atomic numbers. Modern Periodic Table consists of 18 vertical columns called 7 horizontal rows called periods.

Question 3.
How many metals are present in second period of periodic table?
Answer:

Question 4.
The atomic radii of three elements A, B and C of a periodic table are 186 pm, 104 pm and 143 pm respectively. Giving a reason, arrange these elements in the increasing order of atomic numbers in the period.
Answer:
Since atomic size decreases along a period and the atomic number increases. So, the element with smaller radii, has the highest atomic number.

Hence, B has the highest atomic number followed by C and A i.e. A < C < B

Explanation: The atomic size is the distance between the centre of the nucleus and the outermost shell of an isolated atom. The atomic radius is measured in picometre, (1 pm = 10^-12 m).

The atomic radius decreases in moving from left to right along a period. This is due to:
As the atomic number increases, the nuclear charge increases. Increase in nuclear charge tends to pull the electrons closer to the nucleur and reduce the size of the atom.

Question 5.
Consider the following :
20Ca, 8O,16S, 4Be
Which of the above elements would you expect to. be in group 2 of the Modern Periodic table?
Answer:
Consider the electronic configuration of elements:
Ca: 2, 8, 8, 2 O: 2, 6 S: 2, 8, 6 Be: 2, 2
As Ca and Be all have the same number of valence electrons (2), they belong to group 2 of the Modern Periodic Table.

Question 6.
Define electropositivity.
Answer:
Electropositivity is the ability metals to lose electron to form positive ions.
Explanation: Metals have 1, 2, 3 valence electrons and have a strong tendency to lose these to form positive ions, so metal are called electropositive elements.
For example:

as we move down in a group in the periodic table, atomic size increases. As a result, force of attraction between the nucleus and valence electrons decreases.

Question 7.
Write two reasons responsible for the late discovery of noble gases
Answer:
The two reasons for the late discovery of noble gases are:

1. Their low concentration in the atmosphere.
2. Their chemical inertness or very less reactivity.

Question 8.
What were the criteria used by Mendeleev in creating has periodic table
Answer:
The criteria used by Mendeleev in creating his periodic table were the relationship between the atomic masses of the elements and their physical and chemical properties and formulae of the hydrides and oxides formed by an element.

MCQ Questions for Class 10 Science with Answers

Class 10 Science Chemistry MCQ:

• Chemical Reactions and Equations Class 10 MCQ
• Acids, Bases and Salts Class 10 MCQ
• Metals and Non-metals Class 10 MCQ
• Carbon and Its Compounds Class 10 MCQ
• Periodic Classification of Elements Class 10 MCQ