1. Matter in Our Surroundings Class 9 NCERT Exemplar Solutions Chapter 1 (CBSE Science)
CBSE Class 9 Science Chapter 1 : Matter in Our Surroundings – NCERT Exemplar Questions with Answers
Chapter 1 : Matter in Our Surroundings
Multiple Choice Questions
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
Answer: (c) Evaporation, diffusion, expansion of gases .
[ On increasing temperature, particles gain kinetic energy, so evaporation and diffusion become faster, and gases expand due to increased intermolecular movement. ]
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
Answer: (c) Low temperature, high pressure
[Lower temperature reduces kinetic energy, and high pressure brings particles closer, enabling gas liquefaction.]
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
Answer: (c) Gases and liquids behave like fluids .
[ Fluids are substances that can flow, which includes both liquids and gases. Solids do not flow.]
4. During summer, water kept in an earthen pot becomes cool because of the phenomenon of
(a) diffusion (b) transpiration (c) osmosis (d) evaporation
Answer: (d) evaporation
[ Water seeps through pores and evaporates from the pot's surface, using latent heat from the remaining water, thus cooling it. ]
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
Answer: (c) Oxygen, water, sugar
[ Gases (oxygen) have weakest forces, liquids (water) intermediate and solids (sugar) strongest forces of attraction between particles.]
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
Answer: (a) 298 K, 311 K and 339 K
[ We know that, K=°C+273K = °C + 273K =°C+273
We have, 25°C = (25 + 273)K = 298 K
38°C = (38 + 273)K = 311 K
66°C = (66 + 273)K = 339 K ]
7. Choose the correct statement of the following
(a) conversion of solid into vapours without passing through the liquid state is called sublimation.
(b) conversion of vapours into solid without passing through the liquid state is called vapourisation..
(c) conversion of vapours into solid without passing through the liquid state is called freezing.
(d) conversion of solid into liquid is called sublimation.
Answer: (a) conversion of solid into vapours without passing through the liquid state is called sublimation.
[ Sublimation = solid → gas directly (e.g., dry ice or iodine).
Deposition = gas → solid directly.
Freezing = liquid → solid.
Vapourisation = liquid → gas.]
8. The boiling points of diethyl ether, acetone and n-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
Answer: (c) 308 K, 329 K, 391
[ We know that, K = °C + 273.
Diethyl ether: 35°C = (35 + 273)K = 308 K
Acetone: 56°C = (56 + 273) = 329 K
n-Butyl alcohol: 118°C = (118 + 273) = 391 K
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
Answer: (a) Increase in temperature of water
[ Higher temperature gives water molecules more kinetic energy, increasing the rate of evaporation.]
10. In 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)
Answer: (c) (ii) and (iii)
[ Leaking gas reduces molecules (ii), and increasing volume (iii) spreads molecules apart, increasing distance between them.]
Short Answer Questions
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? Comment.
Answer: The water is not pure, because pure water boils at 100°C at normal pressure. The higher boiling point indicates the presence of impurities.
Impurities also affect freezing, so this water will not freeze exactly at 0°C; its freezing point will be slightly lower than 0°C due to the dissolved substances.
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 (Fig. 1.1) would correctly represent the result? Justify your choice.
Answer: The correct option is (d). The temperature remains constant at 0°C because the heat is used to melt the ice (latent heat), not to warm the water. Once all the ice melts, the temperature starts rising.
13. Fill in the blanks:
(a) Evaporation of a liquid at room temperature leads to a——— effect.
(b) At room temperature the forces of attraction between the particles of solid substances are———than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the ——— state. However, there is no order in the ——— state.
(d) ——— is the change of solid state directly to vapour state without going through the ———state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called———.
Answer: (a) Evaporation of a liquid at room temperature leads to a cooling effect.
(b) At room temperature the forces of attraction between the particles of solid substances are stronger than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the liquid state. However, there is no order in the gaseous state.
(d) Sublimation is the change of solid state directly to vapour state without going through the liquid state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called evaporation.
14. Match the physical quantities given in column A to their S I units given in column B :
(A) (B)
(a) Pressure (i) cubic metre
(b) Temperature (ii) kilogram
(c) Density (iii) pascal
(d) Mass (iv) kelvin
(e) Volume (v) kilogram per cubic metre
Answer: (a) Pressure → (iii) pascal
(b) Temperature → (iv) kelvin
(c) Density → (v) kilogram per cubic metre
(d) Mass → (ii) kilogram
(e) Volume → (i) cubic metre
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:
(A) (B)
(a) degree celsius (i) kilogram
(b) centimetre (ii) pascal
(c) gram per centimetre cube (iii) metre
(d) bar (iv) kelvin
(e) milligram (v) kilogram per metre cube
Answer: (a) degree Celsius → (iv) kelvin (temperature)
(b) centimetre → (iii) metre (length)
(c) gram per centimetre³ → (v) kilogram per metre³ (density)
(d) bar → (ii) pascal (pressure)
(e) milligram → (i) kilogram (mass)
16. ‘Osmosis is a special kind of diffusion’. Comment.
Answer: Osmosis is called a special kind of diffusion because it involves the movement of water molecules (solvent) only from a region of low solute concentration to a region of high solute concentration through a semipermeable membrane. Unlike regular diffusion, which can involve any particles and no membrane is needed, osmosis is specific to water and requires a membrane.
17. Classify the following into osmosis/diffusion
(a) Swelling up of a raisin on keeping in water.
(b) Spreading of virus on sneezing.
(c) Earthworm dying on coming in contact with common salt.
(d) Shrinking of grapes kept in thick sugar syrup.
(e) Preserving pickles in salt.
(f) Spreading of smell of cake being baked through out the house.
(g) Aquatic animals using oxygen dissolved in water during respiration.
Answer: (a) Osmosis – Water moves into raisin through its membrane.
(b) Diffusion – Virus particles spread from high to low concentration in air.
(c) Osmosis – Salt draws out water from earthworm’s body cells.
(d) Osmosis – Water moves out of grapes into sugar syrup.
(e) Osmosis – Salt absorbs water from microorganisms, preserving pickles.
(f) Diffusion – Aroma particles spread through air.
(g) Diffusion – Dissolved oxygen moves into aquatic animals’ bodies.
18. Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.
Answer: Ice has a cooling effect because it absorbs latent heat of fusion from the surroundings to melt into water. Steam causes severe burns because it possesses extra latent heat of vaporization which it releases when condensing on the skin, transferring more heat than boiling water at the same temperature.
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. Comment.
Answer: The temperature of the steam is not higher than the boiling water; both are at 100°C (at normal pressure). The intense heat felt by Alka is due to latent heat of vaporisation. Steam carries extra energy used to change water into vapour, and when it touches the skin, this energy is released, causing a burning sensation.
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 (Fig.1.2) would correctly represent the change in its temperature as a function of time.
Answer: The correct graph is (a). Initially, hot water cools to 0°C (downward curve). At 0°C, temperature stays constant as it freezes (horizontal line). After freezing, ice cools further below 0°C (final downward curve).
21. Look at Fig. 1.3 and suggest in which of the vessels A,B, C or D the rate of evaporation will be the highest? Explain.
Answer: Vessel C will have the highest evaporation rate because it has a larger surface area and is exposed to moving air. Increased surface area and wind speed both enhance evaporation by helping more water molecules escape and be carried away quickly.
22. (a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.
(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?
Answer: (a) The conversion of vapour to solid is called deposition.
(b) Latent heat of fusion is the amount of heat energy absorbed by a solid to change into a liquid at its melting point, without any change in temperature. This energy is used to overcome the forces between particles.
Long Answer Questions
23. You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labeled diagram.
Answer: A mixture of naphthalene and ammonium chloride can be separated by sublimation. The mixture is heated in a china dish covered with an inverted funnel. On gentle heating, naphthalene sublimes first and deposits on the cooler inner walls of the funnel. On further heating, ammonium chloride sublimes and deposits separately on another cooler surface. This difference in sublimation temperature helps in separation.
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?
Answer: Priyanshi wearing cotton would be more comfortable. Cotton is breathable and absorbs sweat, allowing it to evaporate and cool the body. Nylon, worn by Ali, is non-absorbent and traps heat and sweat, making it feel sticky and uncomfortable on a hot day.
25. You want to wear your favourite shirt to a party, but the problem is that it is still wet after a wash. What steps would you take to dry it faster?
Answer: To dry the shirt faster, I would wring out excess water first, then hang it in a sunny spot or near a fan. Spreading it out properly increases air contact, and gentle heat from sunlight or a hairdryer speeds up evaporation, helping the shirt dry quickly.
26. Comment on the following statements:
(a) Evaporation produces cooling.
(b) Rate of evaporation of an aqueous solution decreases with increase in humidity.
(c) Sponge though compressible is a solid.
Answer: (a) Evaporation produces cooling:
During evaporation, high-energy particles escape from the liquid surface. The remaining particles lose energy, so the temperature of the liquid decreases, causing cooling.
(b) Rate of evaporation decreases with increase in humidity:
When humidity is high, air already contains more water vapour. So, it cannot take much more vapour, and evaporation slows down.
(c) Sponge though compressible is a solid:
A sponge has tiny air-filled pores. When pressed, air escapes and it gets compressed. But its particles are closely packed and it has a definite shape, so it is a solid.
27. Why does the temperature of a substance remain constant during its melting point or boiling point?
Answer: At the melting point or boiling point, the heat supplied to the substance does not increase its temperature. Instead, this heat is used to change the state of the substance . This energy is called latent heat, and it is used to break the intermolecular forces between particles, so the temperature remains constant.
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