NCERT Exemplar Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings

These Solutions are part of NCERT Exemplar Solutions for Class 9 Science . Here we have given NCERT Exemplar Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings

Multiple Choice Questions

Question 1.
Which one of the following sets of phenomena would increase on raising the temperature ?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gases
(d) Evaporation, solubility, diffusion, compression of gases.
Correct Answer:
(c) All the three phenomenon would increase upon increasing the temperature.

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Question 2.
Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends, she got confused. Help her to identify the correct set of conditions
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure.
Correct Answer:
(c) Both low temperature and high pressure bring the gas molecules closer and help in its liquefaction.

Question 3.
The property to flow is unique to fluids. Which one of the following statements is correct ?
(a) Only gases behave like fluids
(b) Gases and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids.
Correct Answer:
(c) The gases as well as liquids can behave as fluids. There is hardly any fluidity in solids as the particles are very closely packed.

Question 4.
During summer, water kept in an earthen pot becomes cool because of the phenomenon of
(a) diffusion
(b) transpiration
(c) osmosis
(d) evaporation.
Correct Answer:
(d) The evaporation of a liquid is always accompanied by the lowering of temperature and results in cooling.

Question 5.
A few substances are arranged in the increasing order of forces of attraction between their particles. Which one of the following represents a correct arrangement ?
(a) Water, air, wind
(b) Air, sugar, oil
(c) Oxygen, water, sugar
(d) Salt, juice, air
Correct Answer:
(c) It is the correct sequence.

Question 6.
On converting 25°C, 38°C and 66°C to kelvin scale, the correct sequence of temperature will be
(a) 298 K, 311 K and 339 K
(b) 298 K, 300 K and 338 K
(c) 273 K, 278 K and 543 K
(d) 298 K, 310 K and 338 K.
Correct Answer:
(a) It is the correct sequence of temperature obtained by adding 273 K to the given temperature.

Question 7.
Choose the correct statement from the following :
(a) conversion of solid into vapours without passing through the liquid state is called vapourisation.
(b) conversion of vapours into solid without passing through the liquid state is called sublimation.
(c) conversion of vapours into solid without passing through the liquid state is called freezing.
(d) conversion of solid into liquid is called sublimation.
Correct Answer:
(c) It is the correct statement.

Question 8.
The boiling points of diethyl ether, acetone and «-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in kelvin scale ?
(a) 306 K, 329 K, 391 K
(b) 308 K, 329 K, 392 K
(c) 308 K, 329 K, 391 K
(d) 329 K, 392 K, 308 K.
Correct Answer:
(c) It is the correct representation of the boiling points and is obtained by adding 273 K to the given temperature.

Question 9.
Which condition out of the following will increase the evaporation of water ?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water.
Correct Answer:
(a) Increase in temperature always helps in evaporation of a liquid.

Question 10.
Under which of the following conditions, the distance between the molecules of hydrogen gas would increase ?
(i) Increasing pressure on hydrogen contained in a closed container
(ii) Some hydrogen gas leaking out of the container
(iii) Increasing the volume of the container of hydrogen gas.
(iv) Adding more hydrogen gas to the container without increasing the volume of the container.
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv).
Correct Answer:
(c) Both these conditions would increase the distance in the molecules of hydrogen.

Short Answer Questions

Question 11.
A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure ? Will this water freeze at 0°C ?
Under normal temperature and pressure, the boiling point temperature of pure water is 100°C. The boiling point of 102°C means that the given sample is impure and has non-volatile impurities present. This impure sample will have freezing point temperature below 0°C. Please remember that the presence of impurities raises the boiling point tempeature of a liquid and lowers its freezing point.

Question 12.
A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following would correctly represent the result ? Justify your choice.
NCERT Exemplar Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings image - 1
We know that the melting point of ice and the freezing point of water in pure states are both zero. This means that at this temperature, both are present. Upon heating, the temperature would actually not change but heat energy supplied would be absorbed by the ice as latent heat of fusion. This would result in the melting of ice. The temperature would remain zero degree till the whole of ice has melted. Further heating would increase the temperature of water till it starts boiling at 100°C. The curve (d) gives the correct representaton.

Question 13.
Fill in the blanks :

  1. Evaporation of a liquid at room temperature leads to a ……………. effect.
  2. At room temperature, the forces of attraction between the particles of solid substances are …………… than those which exist in the gaseous state.
  3. The arrangement of particles is less ordered in the ……………. state. However, there is no order in the …………… state.
  4. …………….. is the change of gaseous state directly to solid state without going through the state.
  5. The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called …………….


  1. cooling
  2. stronger
  3. liquid, gaseous
  4. freezing, liquid
  5. evaporation.

Question 14.
Match the physical quantities given in column A to their SI units given in Column B.
NCERT Exemplar Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings image - 2
(a)—(iiî), (b)—(iv), (c)—(v), (d)—(ii), (e)—(i).

Question 15.
The non SI and SI units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity :
NCERT Exemplar Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings image - 3
(a)—(iv), (b)—(iii), (c)—(v), (d)—(ii), (e)—(i)

Question 16.
Osmosis is a special kind of diffusion. Comment.
Yes, the statement is true. In both the cases, there is movement of particles. However, osmosis is restricted to only liquid solutions in which the solvent molecules can pass through the pores of a semi-permeable membrane while solute particles are unable to do so. Diffusion is very common in gases and also takes place in liquids. But no semi-permeable membrane is needed in case of diffusion.

Question 17.
Classify the following into osmosis/diffusion

  1. Swelling up of a raisin on keeping in water.
  2. Spreading of virus on sneezing.
  3. Earthworm dying on coming in contact with common salt.
  4. Shrinking of grapes kept in thick sugar syrup.
  5. Preserving pickles in salt.
  6. Spreading of smell of cake being baked through out the house.
  7. Aquatic animals using oxygen dissolved in water during respiration. (C.B.S.E. 2014)


  1. Osmosis
  2. Diffusion
  3. Osmosis
  4. Osmosis
  5. Osmosis
  6. Diffusion
  7. Diffusion.

Question 18.
Water as ice has a cooling effect whereas water as steam may cause severe burns. Explain these observations.
Both ice and steam are the physical states of the same substance i.e. water. However, they differ in their nature. Ice on coming in contact with skin (at a higher temperature) absorbs energy as latent heat of fusion from the skin and melts. Since energy has been taken up from the body, a cooling sensation is experienced. But when steam comes in contact with the skin (lower temperature) it releases energy which causes severe burns on the skin.

Question 19.
Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Explain.
The temperature of both boiling water and steam are the same. However, steam has extra energy in the form of latent heat of vaporisation. That is why, a puff of steam releases more energy than that of boiling water.

Question 20.
A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature (< 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs would correctly represent the change in its temperature as a function of time.
NCERT Exemplar Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings image - 4
The graph (a) gives the correct representation. The temperature of water in the tumbler kept in the freezer compartment gets lowered with time till water changes into ice. At this stage, the temperature becomes 0°C and remains constant till the entire water in the tumbler has frozen. If the tumbler is still kept in the freezer, the temperature will fall below 0°C (negative sign) with passage of time.

Question 21.
Look at the figure and suggest in which of the vessels A, B, C or D, the rate of evaporation will be the highest ? Explain.
NCERT Exemplar Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings image - 6
Vessel B has the smallest size while vessel D is covered. Though vessel A and C are of same size, moving fan will accelerate evaporation. Therefore, the rate of evaporation will be highest in vessel C.

Question 22.
(a) Conversion of solid to vapours is called sublimation. Name the term used to denote the conversion of vapours to solid.
(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion ?
(a) Conversion of vapours to solid is known as freezing.
(b) Conversion of solid state to liquid state is called fusion. The melting point of a solid may be defined as the temperature at which a solid starts melting i.e., starts changing into the liquid state.

Long Answer Questions

Question 23.
You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with a well labelled diagram.
Both naphthalene and ammonium chloride sublime upon heating. Therefore, sublimation technique cannot be used to affect the separation. The separation can be done by dissolving the mixture in completely dry or anhydrous ether taken in a tube. Naphthalene being an organic substance, dissolves in ether whereas ammonium chloride does not dissolve as it is of inorganic nature. The solution formed is immediately filtered (For details, please consult next chapter). Ammonium chloride is left on the filter paper as residue. It is dried and collected. The filtrate is transferred to a china dish and kept in the atmosphere for sometime. Ether readily evaporates as it is a low boiling liquid. The white residue left in the dish is naphthalene. It can be removed and dried. For more details, please consult next chapter.

Question 24.
It is a hot summer day, Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think would be more comfortable and why ?
Priyanshi would be more comfortable than Ali since she is wearing cotton clothes. Being porous in nature, cotton clothes would absorb moisture from the body. As it evaporates, it results in cooling giving comfort to the body. Since Ali is wearing nylon clothes which have hardly any pores, he would feel less comfortable.

Question 25.
Tarun got an invitation to attend a party. On coming to his place, he found that both his shirt and pent were wet. What step he would take to dry them quickly ? (C.B.S.E. 2013)
The wet clothes can be dried in a number of ways.

  1. By spreading them in air under sun so that the water may evaporate.
  2. By spreading them under a fan in a room.
  3. By ironing the clothes. As a result, the moisture present will escape as steam / vapours and the clothes will soon become dry.

Question 26.
Comment on the following statements :

  1. Evaporation produces cooling
  2. Rate of evaporation of an aqueous solution decreases with increase in humidity.
  3. Sponge though compressible is a solid.


  1. As a liquid changes into vapours during evaporation, it needs some energy which it takes from the surroundings. Since the temperature of the surroundings gets lowered, cooling is therefore, caused.
  2. Increase in humidity results in increase in moisture in the atmosphere. As a result, water has less tendency to change into the vapours and rate of evaporation decreases.
  3. Sponge is basically a solid. However, it has very fine holes which are called pin holes. Air gets trapped in these holes and the size of the sponge somewhat increases. On compressing, air escapes from the pores or holes and the size of the sponge decreases.

Question 27.
Why does the temperature of a substance remain constant during its melting point or boiling point ?
As long as a substance has not started either melting or boiling, the heat energy supplied increases the kinetic energy of the particles. Therefore, the temperature of the substance increases. Once it starts melting or boiling, the further heat energy is absorbed either as latent heat of fusion or as latent heat of vaporisation. This does not cause any increase in kinetic energy because all the particles of a substance have sufficient kinetic energy to change into liquid or vapour state. However, interpàrticle forces do not allow them to do so. The energy supplied simply overcomes these interparticle forces and they undergo change in state.

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