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Students can access the CBSE Sample Papers for Class 10 Science with Solutions and marking scheme Set 4 will help students in understanding the difficulty level of the exam.

CBSE Sample Papers for Class 10 Science Set 4 for Practice

Time: 3 Hours
Maximum Marks: 80

General Instructions:

(i) The question paper comprises four sections A, B, C and D. There are 36 questions in the question paper. All questions are compulsory.
(ii) Section-A – question no. 1 to 20 – all questions and parts there of are of one mark each.
These questions contain multiple choice questions (MCQs), very short answer questions and assertion – reason type questions. Answers to these should be given in one word or one sentence.
(iii) Section-B – question no. 21 to 26 are short answer type questions, carrying 2 marks each. Answers to these questions should in the range of 30 to 50 words.
(iv) Section-C – question no. 27 to 33 are short answer type questions, carrying 3 marks each.
Answers to these questions should in the range of 50 to 80 words. :
(v) Section—D – question no. – 34 to 36 are long answer type questions carrying 5 marks each. Answer to these questions should be in the range of 80 to 120 words.
(vi) There is no overall choice. However, internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions.
(vii) Wherever necessary, neat and properly labelled diagrams should be drawn.

Section-A

1. What is the radius of curvature of a plane mirror?

2. Why is red colour selected for danger signal lights?

3. What is the cause of dispersion of light by prism.
OR
Why does the sky appear dark instead of blue to an astronaut?

4. Name the components of blood which transport:
(i) Food, carbon dioxide and nitrogeneous wastes
(ii) Oxygen

5. Write the relationship between heat energy produced in a conductor when potential difference V is applied across its terminals and a current, I flows through it for the time ‘F.

6. A beam of light is incident through the holes on side A and emerges out of the hole on the other face of the box as shown in the figure. What type of lens could be inside the box?

7. Why do stars twinkle?

8. A lens forms an image at Y of an object at X. Where does the lens form an image of an object at P?

9. What indication do we get by appearance of dwarf plant in F2 generation?
OR
What is sex of the baby that inherits Y-chromosome from the father?

10. If a women is using copper-T, will it help in protecting against sexually transmitted diseases?
OR
Why is temperature of scrotal sac 2°C less than the body temperature?

11. Name the intermediate and the end products of glucose breakdown on aerobic respiration.

In the experiment “Chlorophyll is necessary for photosynthesis’, why does the green part of variegated leaf turns blue black after putting in iodine solution?

12. Out of Li and K, which one have stronger metallic character and why?
OR
The formula of magnesium oxide is MgO. State the formula of barium nitrate and barium sulphate, if barium belongs to the same group.

13. X + YSO₄ → XSO₄ + Y
Y + XSO₄ → No reaction
Out of two elements, ‘X’ and ‘Y’ which is more reactive and why?

Assertion (A) and Reason (R)
For question numbers 14,15 and 16, two statements are given- one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (i), (iii) and (iv) as given below:

(i) Both A and R are true, and R is correct explanation of the assertion.
(ii) Both A and R are true, but R is not the correct explanation of the assertion.
(iii) A is true, but R is false.
(iv) A is false, but R is true.

14. A. Copper sulphate solution turns blue litmus red.
R. Copper sulphate is salt of strong acid H₂SO₄, weak base Cu(OH)₂, therefore, acidic in nature.
Answer:
(i)

15. A. The angle of incidence and reflection are equal.
R. The angle between incidence ray and normal is called angle of incidence.
Answer:
(ii)

16.
R. It is a combination reaction because CO combines with H₂ to form CH₃OH i.e. two substances combine to form a single compound.
OR
1. The reaction, MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂ is an example of redox reaction.
2. In this reaction, HCl is reduced to Cl₂ whereas MnO₂ is oxidized to MnCl.
Answer:
(ii) OR (iii)

Answer Q. No 17 – 20 contain five sub-parts each. You are expected to answer any four sub­parts in these questions.

17. Read the following and answer any four questions from 17 (i) to 17 (v) (4 × 1 = 4)

The growing size of the human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organisms increase their population. The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on.

Some degree of sexual maturation does not necessarily mean that the mind or body is ready for sexual acts or for having and bringing up children. Various contraceptive devices are being used by human beings to control the size of population.

(i) Which of the following is not a common sign of sexual maturation in boys and girls.
(a) Pubic hair
(b) Menstrual cycle in females
(c) Broad shoulders in females
(d) Wider chest in males
Answer:
(c) Broad shoulders in females

(ii) Which contraceptive method changes the hormonal balance of the body?
(a) Condoms
(b) Orals pills
(c) IUCD
(d) None of these
Answer:
(b) Orals pills

(iii) Sex ratio of females/1000 males in different states are as follows:

States	2013-15	2012-14
Delhi	869	876
Haryana	831	866
Uttar Pradesh	879	869
Punjab	889	870

Name the state which improves the ratio to maximum extent in 2013-15.
(a) Delhi
(b) Haryana
(c) Uttar Pradesh
(d) Punjab
Answer:
(d) Punjab

(iv) According to the tabel in above question, which state declines this ratio to maximum extent in 2013-15.
(a) Delhi
(b) Haryana
(c) Uttar Pradesh
(d) Punjab
Answer:
(b) Haryana

(v) What is the major cause of less females than males in India?
(a) Males live longer than females
(b) Naturally, male child birth rate is higher than female child
(c) Female foeticide
(d) None of these
Answer:
(c) Female foeticide

18. Read the following and answer any four questions from 18 (i) to 18 (v) (4 × 1 = 4)
The data for four elements is given below:

Element	Carbon	Nitrogen	Fluorine	Neon
Symbol	C	N	F	Ne
Structure	Macromolecular	Simple molecules N7	Simple molecules F,	Single atoms Ne
Boiling point/°C	4200	-196	-188	-246

(i) Name the element that is solid at room temperature.
(a) Carbon
(b) Nitrogen
(c) Fluorine
(d) Neon
Answer:
(a) Carbon

(ii) Why is the boiling point of carbon the highest?
(a) Carbon atoms linked through strong ionic bonds to form molecules.
(b) Carbon atoms are close together with strong covalent bonds.
(c) Carbon atoms are small in size thus have more stronger attractions among them.
(d) Carbon atoms are not linked to each other.
Answer:
(b) Carbon atoms are close together with strong covalent bonds.

(iii) Which of the following element is inert?
(a) Carbon
(b) Nitrogen
(c) Fluorine
(d) Neon
Answer:
(d) Neon

(iv) Carbon has many allotropes with macromolecular structure. Which of the following is not such kind of allotrope of carbon?
(a) Diamond
(b) Fullerene
(c) Graphite
(d) Coke
Answer:
(d) Coke

(v) Which of the following is the most reactive element?
(a) Carbon
(b) Nitrogen
(c) Fluorine
(d) Neon
Answer:
(c) Fluorine

19. Read the following and answer any four questions from 19 (i) to 19 (v) (4 × 1 = 4)

(i) What is the range of resistivity in metals which are conductor of electricity?
(a) 10^-8 to 10^-7 Ωm
(b) 10^-7 to 10^-6 Ωm
(c) 10 ⁸ to 10^-6 Qm
(d) 10 ⁸ to 10 ⁴ Qm
Answer:
(c) 10 ⁸ to 10^-6 Qm

(ii) Why are alloys used in heating devices like electric iron, toasters, immersion rods, etc.?
(1) Alloys have high resistivity.
(2) Alloys do not oxidise or bum at high temperature.
(3) Alloys have high conductivity thus allow high current through it
(a) III only
(b) I only
(c) II and III
(d) I and II
Answer:
(d) I and II

(iii) Which of the following is used in transmission wires?
(a) Cu
(b) Al
(c) Zn
(d) Fe
Answer:
(d) Fe

(iv) Which is the best conducting metal?
(a) Cu
(b) Ag
(c)  Au
(d) Hg
Answer:
(d) Hg

(v) Based on resistivity, which of the following is better to use as insulation to protect us from electric current.
(a) Glass
(b) Hard rubber
(c) Nichrome
(d) Diamond
Answer:
(c) Nichrome

20. Read the following and answer any four questions from 20 (i) to 20 (v)  (4 × 1 = 4)

When a single parent is involved in the formation of a new individual, without the fusion of gametes, it is called asexual reproduction. It involves repeated mitotic divisions.

Sexual reproduction is a process of combining DNA from two different individuals during reproduction. This is brought about by the fusion of the male and female gametes.

(i) The type of reproduction taking place is

(a) Budding
(b) Fragmentation
(c) Regeneration
(d) Fission
Answer:
(c) Regeneration

(ii) Choose the right option

A		B	C	D	E
(a)	Fallopian tube	Oviduct	Uterus	Cervix	Vagina
(b)	Oviduct	Vas deferens	Ovary	Vagina	Cervix
(c)	Ovary	Oviduct	Uterus	Cervix	Vagina
(d)	Ovary	Fallopian tube	Uterus	Vagina	Cervix

Answer:
(c)

(iii) Where does fertilisation occur in human females?
(a) Uterus
(b) Cervix
(c) Oviduct
(d) None of these
Answer:
(d) None of these

(iv) The simple animals like Planaria can be cut into a number of pieces and each piece grows into a complex organism. What is the process known as?
(a) Budding
(b) Fragmentation
(c) Spore formation
(d) Regeneration
Answer:
(d) Regeneration

(v) Spirogyra reproduces by
(a) Fission
(b) Regeneration
(c) Fragmentation
(d) Budding
Answer:
(c) Fragmentation

Section-B

21. Identify the type of magnetic field represented by the magnetic field lines given below and name the type of conductors which can produce them.

22. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below:

I (amperes)	0.5	1.0	2.0	3.0	4.0
V (volts)	1.6	3.4	6.7	10.2	13.2

Plot a graph between V and I and calculate the resistance of that resistor.
Answer:
3.314 Ω

23. You have three test tubes. One of them contains distilled water and the other two contain an acidic and a basic solution, respectively. If you are given only red litmus paper; how will you identify the contents of each test tube?
OR
Equal lengths of magnesium ribbon 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?

24. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of reaction.

25. A ray of light incident on rectangular glass slab emerges parallel to itself. Draw a labelled diagram to justify this statement.
OR
Define absolute refractive index. Mention its unit. Can the value of absolute refractive index be smaller than 1 ? Justify your answer.

26. How does the metallic character of elements changes along a period of the periodic table from left to right and why?

Section – C

27. Show the path of the reflected ray, after reflection in each case.

(i) Draw a diagram of human alimentary canal and label on it:
Oesophagus, Gall bladder, Liver and Pancreas

(ii) Explain the statement, “Bile does not contain any enzyme, but it is essential for digestion.”
OR
How respiration does takes place in plants?

29. Based on the group valency of elements, state the formula of the following, giving justification for each.
(i) Oxides of Group 1 elements.
(ii) Halides of the elements of Group 13.
(iii) Compounds formed when an element of group 2 combines with an element of Group 16.

30. A magnetic compass needle is placed in the plane of paper near point A as shown in the figure. In which plane should a straight current carrying conductor be placed so that it passes through A and there is no change in the “A deflection of the compass? Under what conditions is the deflection maximum and why?

31. (i) What is the nature of food coming from stomach?
(ii) Mention any two structural modifications in small intestine which helps in absorption of food.

32. An electron enters a magnetic field, at right angle to the field direction.
(i) State the rule to find the direction of force acting on the electron.

(ii) What will be the direction of force acting on the electron, in the above case?

33. (i) Two conductors A & B of resistance 5 ohms and 10 ohms respectively can be arranged in parallel and later on in series. In each arrangement, the total voltage applied is 120V. In which arrangement will the voltage across A and B be the same and in which case will the current flowing through A and B be the same?
(ii) Calculate the total resistance of each arrangement.
Answer:
(ii) (a) 3.33Ω
(b) 15Ω

Section-D

34. The structural formula of five compounds are given below.

(i) Which two compounds belong to the same homologous series?
(ii) Which compound belongs to the same homologous series as ethanol?
(iii) Which compound on hydrogenation produces E?
(iv) Which compound when dissolved in water turns blue litmus red?
(v) Name the homologous series for compound B.

35. (i) Identity A, B, C and D in the given diagram and write their names.

(ii) What is pollination? Explain its significance.
(iii) Explain the process of fertilisation in flowers. Name the parts of the flower that develop after fertilisation into
(a) seed
(b) fruit
OR
(i) Draw the diagram of female reproductive system and match and mark the part (s):
(a) Where block is created surgically to prevent fertilisation.
(b) Where CuT is inserted.
(c) Inside which condom can be placed.
(ii) Why do more and more people prefer to use condoms? What is the principle behind use of condoms?

36. (i) Name the organisms which belong to first and third trophic level in food chain comprising of the following:
Insects, birds, frog and grass.
(ii) What will happen if we kill all the organisms in one trophic level?
OR
(i) Give reason to justify the following:
(a) The existence of decomposers is essential in a biosphere.
(b) Flow of energy in a food chain is unidirectional.
(ii) Why is improper disposal of waste a curse to environment?

Students can access the CBSE Sample Papers for Class 10 Science with Solutions and marking scheme Set 1 will help students in understanding the difficulty level of the exam.

CBSE Sample Papers for Class 10 Science Set 1 with Solutions

Time: 3 Hours
Maximum Marks: 80

General Instructions:

(i) The question paper comprises four sections A, B, C and D. There are 36 questions in the question paper. All questions are compulsory.
(ii) Section-A – question no. 1 to 20 – all questions and parts there of are of one mark each.
These questions contain multiple choice questions (MCQs), very short answer questions and assertion – reason type questions. Answers to these should be given in one word or one sentence.
(iii) Section-B – question no. 21 to 26 are short answer type questions, carrying 2 marks each. Answers to these questions should in the range of 30 to 50 words.
(iv) Section-C – question no. 27 to 33 are short answer type questions, carrying 3 marks each.
Answers to these questions should in the range of 50 to 80 words. :
(v) Section—D – question no. – 34 to 36 are long answer type questions carrying 5 marks each. Answer to these questions should be in the range of 80 to 120 words.
(vi) There is no overall choice. However, internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions.
(vii) Wherever necessary, neat and properly labelled diagrams should be drawn.

Section – A

Question 1.
A women gave birth to a girl. Name the chromosome from sperm responsible for the offspring.
Answer:
Sperm with X chromosome from male is responsible for the birth of female and Y chromosome would be responsible for the male offspring. So for the given case, X chromosome from sperm is responsible for the offspring.

Question 2.
Name the gases which have replaced CFCs.
Answer:

• HFCs (Hydrofluorocarbons)
• Perfluorocarbons (PFCs) have replaced CFCs.

Question 3.
When calcium oxide is added to water, it completely dissolves in water without forming bubbles. What product is formed in this reaction?
Answer:
Ca(OH)₂

Question 4.
A plant gets rid of excess water through transpiration. What is the method used by plants to get rid of solid waste products?
Answer:
Shedding of yellow leaves

Question 5.
In peas, a pure tall plant (TT) is crossed with a short plant (tt). What is the ratio of pure tall plants to short plants in F2?
Answer:
3 : 1

Question 6.
State the direction of magnetic field in the following case.
Answer:

Perpendicular to the plane of paper in the outward direction by using Fleming’s left hand rule.

Question 7.
Why covalent compounds have low melting and boiling points?
OR
What is catenation?
Answer:
As the bond is formed by sharing of electrons between two atoms. Intermolecular forces are small between the covalent compounds. These bonds break easily.
OR
Carbon has the unique ability to form bonds with the other atoms of carbon which gives rise to large molecules. This property of self linking is called catenation.

Question 8.
What is the formula of oxide and hydride of Group I elements?
OR
What are isotopes?
Answer:
Oxide formula → R₂O; Hydride formula → RH.
‘R’ represents Group I element. F-31
OR
Isotopes are the atoms of same element having same atomic number but different mass number.

Question 9.
Why are the rings of cartilage present in air tube—Trachea?
OR
In what form is food energy stored in plants and animals?
Answer:
Rings of cartilage prevents the trachea from collapsing.
OR
Plants—Starch; Animals—Glycogen.

Question 10.
List two functions performed by the testis in human beings.
OR
What happens when a mature spirogyra filament attains considerable length?
Answer:

• To produce sperms
• To produce male sex hormone/testosterone

OR
Its filament breaks up into smaller fragments or pieces, and each fragment grows into a new filament/individual.

Question 11.
Name two human traits that show variations.
OR
How does the creation of variations in a species promote survival?
Answer:
Colours of eyes and shape of external ears.
OR
Variations increases the adaptability of an organism to its changing environmental conditions.

Question 12.
What is silvering of mirror?
Answer:
Silvering of mirror means coating the surface of mirror with a thin layer of silver, aluminium or some other shiny, opaque material.

Question 13.
Write the two raw materials for making food, used by living organisms of first tropic level.
Answer:
CO₂ and Water

Assertion (A) and Reason (R)
For question numbers 14,15 and 16, two statements are given- one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (i), (ii), (iii) and (iv) as given below:

(i) Both A and R are true, and R is correct explanation of the assertion.
(ii) Both A and R are true, but R is not the correct explanation of the assertion.
(iii) A is true, but R is false.
(iv) A is false, but R is true.

Question 14.
A. Magnetic field lines have both direction and magnitude.
R. The field lines, emerge from the north pole and merge at south pole
OR
A. Compass is a small magnet and gives direction of magnetic field lines.
R. It gets deflected when brought near a bar magnet.
Answer:
(ii) OR (i)

Question 15.
A. Copper does not displace hydrogen from dilute acids.
R. Copper is less reactive than hydrogen.
Answer:
(i)

Question 16.
A. When two resistances of 4 Ω are connected in parallel total resistance is 2 Ω.
R. When two resistances of 4 Ω are connected in series total resistance is 8 Ω.
Answer:
(ii)

Answer Q. No 17 – 20 contain five sub-parts each. You are expected to answer any four sub­parts in these questions.

Question 17.
Read the following and answer any four questions from 17 (i) to 17 (v) (4 × 1 = 4)
The table below shows the results of different experiment conducted on two acids X and Y of equal concentration:

	X	Y
Conductivity of Solution	400 S m1	7.0 S m1
Temperature change when excess acid reacted with 100 mL of 1.0 M NaOH solution	6.9°C	6.7°C
Reaction with Mg	Hydrogen gas is produced rapidly with rapid effervescence	Hydrogen gas is produced slowly with gradual effervescence

(i) Which of the following statement is correct?
(a) X is stronger acid because it has higher conductivity.
(b) Y is stronger acid because hydrogen is produced slowly when reacts with Mg.
(c) X is weaker acid because temperature change is higher when reacts with NaOH.
(d) Y is weaker acid because is has higher conductivity.
Answer:
(a) X is stronger acid because it has higher conductivity.

(ii) Select the correct relation from the following:
(a) (H+) x < (H+)y
(b) (pH) x < (pH)Y
(c) (H+) x = (H+)Y
(d) (PH) y > 7
Answer:
(b) (pH) x < (pH)Y

(iii) What will be colour of universal indicator in ‘X’?
(a) Blue
(b) Orange
(c) Green
(d) Red
Answer:
(d) Red

(iv) How many moles of H2 gas will be liberated by ‘X’ and ‘Y’ during reaction with 1 mole of Mg?
(a) 1/2
(b) 1/4
(c) 2
(d) 1
Answer:
(d) 1

(v) The gas formed when X and Y reacts with a metal carbonate is:
(a) Hydrogen
(b) Hydrogen Sulphide
(c) Oxygen
(d) Carbon dioxide
Answer:
(d) Carbon dioxide

Question 18.
Read the following and answer any four questions from 18 (i) to 18 (v) (4 × 1 = 4)
Answer:
Ohm’s law gives the relationship between current flowing through a conductor with potential difference across it provided the physical conditions and temperature remains constant. The electric current flowing in a circuit can be measured by an ammeter.

Potential difference is measured by voltmeter connected in parallel to the battery or cell. Resistances can reduce current in the circuit. A variable resistor or rheostat is used to vary the current in the circuit.

(i) Graphs between electric current and potential difference across two conductors A and B are shown in the figure. Which of the following conductor has more resistance?

(a) B
(b) A
(c) Both have equal resistance
(d) None of these
Answer:
(b) A

(ii) Seven identical lamps of resistance 220 Ω each are connected to a 220 V line as shown in figure. Then reading of the ammeter will be:

(a) \(\frac{1}{10} \mathrm{~A}\)
(b) \(\frac{2}{5} \mathrm{~A}\)
(c) \(\frac{3}{10} \mathrm{~A}\)
(d) None of there
Answer:
(d) None of there

(iii) For metallic conductor voltage uses current graph is shown at two different temperatures T₁ and T₂. From the graph it follows:

(a) T₁ = T₂
(b) T₁ > T₂
(c) T₁ < T₂
(d) None of above
Answer:
(c) T₁ < T₂

(iv) If the resistance of wire A is four times resistance of wire B then the ratio of cross sectional areas of wires is
(a) 1:2
(b) 1:4
(c) 1:8
(d) 1:6
Answer:
(b) 1:4

(v) Ohm’s law is valid only when
(a) Temperature increases
(b) Temperature decreases
(c) Graph between V and I is a straight line
(d) Pressure remains constant.
Answer:
(c) Graph between V and I is a straight line

Question 19.
Read the following and answer any four questions from 19 (i) to 19 (v) (4 × 1 = 4)
Answer:
A student took HC1 in a conical flask and was placed on a white tile with cross mark. When seen through the flask the mark was visible. On adding some sodium thiosulphate in the flask the cross marked disappeared when seen through the flask. The student observed some reaction as

(i) Name the type of reaction seen in the setup.
(a) Redox reaction
(b) Precipitation reaction
(c) Displacement reaction
(d) Double displacement reaction
Answer:
(b) Precipitation reaction

(ii) Why did the cross mark disappear?
(a) The insoluble precipitate that is formed in the flask does not allow the light to pass through it to see the cross mark.
(b) The resultant solution is dark coloured which does not allow the light to pass through it.
(c) The resultant solution has high viscosity due to which it refracts the light to other angle.
(d) The solution so formed has ability to absorb black colour hence black coloured cross is not seen.
Answer:
(a) The insoluble precipitate that is formed in the flask does not allow the light to pass through it to see the cross mark.

(iii) Give the chemical formula of the gas formed in the reaction.
(a) SO₂
(b) SO₃
(c) O₂
(d) Cl₂
Answer:
(a) SO₂

(iv) Name the resultant insoluble substance formed in the flask.
(a) Sodium sulphide
(b) Sodium sulphate
(c) Sodium sulphite
(d) Sulphur
Answer:
(d) Sulphur

(v) Which of the following reaction is of similar type as observed in the given set up.

Answer:
(a)

Question 20.
Read the following and answer any four questions from 20 (i) to 20 (v) (4 × 1 = 4)
Answer:
Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow, without doing any calculations:

S. No.	Object distance u (cm)	Image distance v (cm)
1	-90	+ 18
2	-60	+ 20
3	-30	+ 30
4	-20	+ 60
5	-18	+ 90
6	-10	+ 100

(i) What is the focal length of the convex lens? Give reason in support of your answer.
(a) -10
(b) +10
(c) -15
(d) +15

(ii) Write the serial number of that observation which is not correct.
(a) S.No. 1
(b) S.No. 4
(c) S.No. 3
(d) S.No. 6

(iii) The approximate value of magnification in case of S.No. 4 is
(a) -2
(b) -3
(c) +3
(d) +2

(iv) The image formed in case of S.No. 2 is
(a) virtual and enlarged
(b) virtual and diminished
(c) real and diminished
(d) real and enlarged

(v) If a convex lens is used to focus sunlight on a paper, where the paper should be placed so that it catches fire.
(a) At centre of curvature
(b) At principal focus.
(c) At optical centre of lens
(d) At 25 cm away from lens
Answer:
(i) (d) From S.No.3 we can say that the radius of curvature of the lens is 30 cm because when an object is placed at the centre of curvature of a convex lens its image is formed on the other side of the lens at the same distance from the lens. And, we also know that focal length is half of the radius of curvature. Thus, focal length of the lens is + 15 cm.

(ii) (d) S.No.6 is not correct as the object distance is between focus and pole, so for such cases the image formed is always virtual but in this case it is written that a real image is formed as the image distance is positive.

(iii) \(\text { (b) } m=\frac{v}{u}=\frac{+60}{-20}=-3\)

(iv) (c)

(v) (b)

Section-B

Question 21.
A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 18 cm at a distance of 12 cm from it. Use lens formula to determine the position, size and nature of image formed.

The image formed is on the same side as the object, at a distance of 36 cm from the optical centre. The -ve sign shows that the image is virtual.
\(m=\frac{h_{i}}{h_{o}}=\frac{v}{u}=\frac{-36}{-12}=3\)
h₀ – 5 cm, then h_i = 3 x 5 = 15 cm The image is three times larger than the size of the object.

Question 22.
How is bleaching powder prepared? Give its chemical equation and write its two uses.
OR
A white coloured powder is used by doctors for supporting fractured bones.
(i) Write chemical name and formula of the powder
(ii) When this white powder is mixed with water a hard solid mass is obtained. Write balanced chemical equation for the change.
Answer:
Preparation: On passing chlorine gas through a test tube containing dry slaked lime Ca(OH)₂, bleaching powder is prepared.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Uses:
(i) It is used as. bleaching agent in textile industry and paper factories.
(ii) It is used as an oxidising agent in many industries.
OR
(i) Calcium sulphate hemihydrate, \(\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}\)
(ii) \(\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}+\frac{3}{2} \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\)

Question 23.
(i) Choose the amphoteric oxides from the following oxides.
Na₂O, ZnO, Al₂O₃, CO₂, H₂O.

(ii) Why is it that non-metals do not displace hydrogen from dilute acids?
Answer:
(i) Al₂O₃, H₂O and ZnO are amphoteric oxides.
(ii) Non-metals cannot loose electrons so that H⁺ ions from acids become hydrogen gas and thus, cannot be displaced.

Question 24.
Find the current drawn from the battery by the network of four resistors shown in the figure.
Answer:

Equivalent resistance of the given network is

Question 25.
An element ‘E’ has following electronic configuration:

(i) To which group of the periodic table does element ‘E’ belong?
(ii) To which period of the periodic table does element ‘E’ belong?
(iii) State the number of valence electrons present in element ‘E’
(iv) State the valency of the element ‘E’
Answer:
(i) ‘E’ belongs to group 16
(ii) It belongs to 3rd period
(iii) It has 6 valence electrons
(iv) Its valency is equal to 2

Question 26.
Why is respiration considered as exothermic reaction? Explain.
OR
(i) Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?

(ii) What change in colour is observed when silver chloride is left exposed to sunlight? What type of chemical reaction is this?
Answer:
In respiration, glucose gets oxidized to form carbon dioxide, water and heat is evolved.
As heat energy is released during respiration it is regarded as an exothermic reaction.
OR
(i) It is because properties of compound (H₂O) are different from properties of its constituting elements, i.e., H₂ and O₂.
(ii) Silver turns black, the reaction is decomposition.

Section – C

Question 27.
Leaves of healthy potted plants were coated with vaseline to block the stomata. Will this plant remain healthy for long? State 3 reasons for your answer.
Answer:
No, this plant will not stay healthy for long. The plant will start dying because:

• Stomata gets blocked and no exchange of gases takes place.
• No intake of CO₂ for photosynthesis and O₂ for respiration.
• No transpiration and hence water transportation will be affected.

Question 28.
Describe briefly the three ways in which individual with a particular trait may increase in population.
Answer:

• Variation helps in survival of individuals.
• Sexual reproduction results in variation.
• Adaptation and natural selection.

Question 29.
How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:
Mendel conducted a monohybrid cross with pea plants, and he observed that one of the contrasting characters disappears in F₁ generation. This character reappears in F₂ generation (obtained by selfing F₁) in just 25% of the progeny.

Mendel conclude that the character which expresses itself in F₁ is the dominant character while the other one which is not able to express in F₁ individuals is recessive character. This recessive character is able to express only in its pure form i.e. in 25% of F₂ individuals.

Question 30.
Study the given flow chart and answer the below given questions.

(i)
(a) Which form of the Sun’s energy is trapped by the producer?
(b) Into which energy form is the Sun’s energy converted when it is trapped by the producer?

(ii)
(a) Calculate X in the flow chart.
(b) Calculate Y on the flow chart.
(c) Label the above box on flow chart.
Answer:
(i)
(a) Light (or solar) energy
(b) Chemical energy

(ii)
(a) 1200 units
(b) 48 units
(c) Decomposers like bacteria or fungi.

Question 31.
Samples of four metals A,B, C and D were taken and added to the following solutions one by one. The results obtained have been tabulated as follows.

Metal	Iron (II) sulphate	Copper (II) sulphate	Zinc sulphate	Silver nitrate
A	No reaction	Displacement	—	—
B	Displacement	—	No reaction	—
C	No reaction	No reaction	No reaction	Displacement
D	No reaction	No reaction	No reaction	No reaction

Use the table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of copper (II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer:
(i) B is most reactive.
(ii) Blue colour of copper sulphate solution disappears and reddish brown copper metal is deposited on the metal B.
(iii) B > A > C > D is the order of reactivity.

Question 32.
Foetus derives its nutrition from the mother.
(i) Identify the tissue used for above purpose. Explain its structure.
(ii) Explain how wastes generated by developing embryo are removed.
(iii) How does the birth of child take place?
Answer:
(i) Placenta is a special tissue connection between embryo and uterine wall. It acts as an endocrine gland. It possesses villi that increases the surface area for absorption of nutrients. Facilitates passage of nutrition and oxygen to embryo from mother through blood.

(ii) Waste substances produced by embryo are removed through placenta into mother’s blood.

(iii) Birth of child takes place after the gestation period (9 months inside the womb of mother). When the pain in the uterine walls is at highest then the birth of child takes place by the birth canal.

Question 33.
(i) Show the formation of Na₂O by transfer of electrons between the combining atoms.
(ii) Why are ionic compounds usually hard?
(iii) How is it that ionic compounds in the solid state do not conduct electricity, but they do so when in molten state?
OR
(i) Which product is formed in the chemical reaction between a small strip of magnesium and nitric acid?
(ii) What happens when a pellet of sodium is dropped in water?
(iii) Identify the ‘X’ in the given reaction: P₄(s) + SO₂(g) → X
Answer:

(ii) Ionic compounds are hard due to strong force of attraction between oppositely charged i0ns.

(iii) In solid-state, ions are not free to move, whereas in molten state ions are free to move. Therefore, they conduct electricity in a molten state.
OR
(i) Mg(NO₃)₂ and 2H₂
(ii) It catches fire and forms sodium hydroxide
(iii) P₄O₁₀(s)

Section-D

Question 34.
(i) Write the functions of the following parts in human female reproductive system:
(a) Ovary
(b) Oviduct
(c) Uterus

(ii) Describe the structure and function of placenta.
OR
What is binary fission in organisms? With the help of suitable diagrams, describe the mode of reproduction in amoeba.
Answer:
(i) (a) Ovary –
• Production of female hormone
• Production of female gamete

(b) Oviduct –
• Transfer of female gamete from the ovary
• Site of fertilization

(c) Uterus –
• Implantation of the zygote
• Nourishment of the developing embryo/placenta formation.

(ii) Structure of Placenta: It is a disc-like structure embedded in the uterine wall, connected to the embryo. It has villi on the embryo’s side of the tissue and on the mother side it has blood spaces, which surround the villi.

(iii) (a) Circuit diagram

V	I = V/R	V/I
0.8 V	0.8/2.67 = 0.30	8/3
1.2 V	1.2/2.67 = 0.45	8/3
1.6 V	1.6/2.67 = 0.60	8/3

Conclusion: ‘R’ is constant at given temperature. VI graph shows straight line.

Question 36.
(i) A thin converging lens forms a
(a) Real magnified image.
(b) Virtual magnified image of an object place in front of it.
Write the positions of the object in each case.
(ii) Draw a labelled ray diagram to show the image formation in each case.
(iii) How will the following be affected on cutting this lens into two halves along the principal axis?
(a) Focal length
(b) Intensity of image formed by half lens.
OR
Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow, without doing any calculations:

S.No.	Object distance u (cm)	Image distance v (cm)
1	-90	+ 18
2	-60	+ 20
3	-30	+ 30
4	-20	+ 60
5	– 18	+ 90
6	– 10	+ 100

(i) What is the focal length of the convex lens? Give reason in support of your answer.
(ii) Write the serial number of that observation which is not correct. How did you arrive at this conclusion?
(iii) Take an appropriate scale to draw a ray diagram for the observation at S. No. 4 and find the approximate value of magnification.
Answer:
(i) (a) When the object is placed between ‘F’ and ‘2F’
(b) When the object is placed between pole ‘P’ and ‘F’

(ii)

(iii) No, focal length will remain the same because radius of curvature remains the same. Therefore, intensity of the image will decrease.
OR

(i)  From S.No.3 we can say that the radius of curvature of the lens is 30 cm because when an object is placed at the centre of curvature of a convex lens its image is formed on the other side of the lens at the same distance from the lens. And, we also know that focal length is half of the radius of curvature. Thus, focal length of the lens is + 15 cm.

(ii) S.No.6 is not correct as the object distance is between focus and pole, so for such cases the image formed is always virtual but in this case it is written that a real image is formed as the image distance is positive which is not possible.

(ii) Approximate value of magnification for object distance – 20 cm and image distance + 60 cm is 3.