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NCERT Exemplar · Class 9 Science Matter in Our Surroundings

27 questions · 27 still being checked

Multiple Choice Questions 1–10 (part 1 of 3)

  1. Exercise 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

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    NCERT’s answer
    (c)
    (c) Evaporation, diffusion, expansion of gases.\[T\uparrow \;\Rightarrow\; KE_{avg}\uparrow \;\Rightarrow\; v_{particle}\uparrow \]Faster particles escape the liquid surface, mix into neighbouring space and push a gas's volume outward. Compression needs applied pressure, not heat, so it does not rise with temperature.

  2. Exercise 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

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    NCERT’s answer
    (c)
    (c) Low temperature, high pressure.\[T\downarrow \;\Rightarrow\; KE_{avg}\downarrow \qquad P\uparrow \;\Rightarrow\; \text{intermolecular spacing}\downarrow \]With particles slower and pushed closer, the attraction between them can now hold the compressed gas together as a liquid.

  3. Exercise 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

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    NCERT’s answer
    (c)
    (c) Gases and liquids behave like fluids.Particles in gases and liquids slide past one another and take the shape of their container; solid particles stay locked in place and cannot flow.

  4. Exercise 4

    During summer, water kept in an earthen pot becomes cool because of the
    phenomenon of
    (a)
    diffusion
    (b)
    transpiration
    (c)
    osmosis
    (d)
    evaporation

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    NCERT’s answer
    (d)
    (d) Evaporation.Water seeping through the porous earthen walls evaporates from the outer surface, and evaporation draws latent heat from the water left behind, cooling the pot.

  5. Exercise 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

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    NCERT’s answer
    (c)
    (c) Oxygen, water, sugar.Oxygen is a gas, water a liquid and sugar a solid; the force of attraction between particles increases in exactly that order,\[\text{gas} < \text{liquid} < \text{solid} \]

  6. Exercise 6

    On converting 25\displaystyle 25°C, 38\displaystyle 38°C and 66\displaystyle 66°C to kelvin scale, the correct sequence of
    temperature will be
    (a)
    298\displaystyle 298 K, 311\displaystyle 311 K and 339\displaystyle 339 K
    (b)
    298\displaystyle 298 K, 300\displaystyle 300 K and 338\displaystyle 338 K
    (c)
    273\displaystyle 273 K, 278\displaystyle 278 K and 543\displaystyle 543 K
    (d)
    298\displaystyle 298 K, 310\displaystyle 310 K and 338\displaystyle 338 K

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    NCERT’s answer
    (a)
    (a) $\displaystyle 298$ K, $\displaystyle 311$ K and $\displaystyle 339$ K.\[K = {}^\circ\text{C} + 273 \] \[25\,{}^\circ\text{C} + 273 = 298\text{ K} \] \[38\,{}^\circ\text{C} + 273 = 311\text{ K} \] \[66\,{}^\circ\text{C} + 273 = 339\text{ K} \]

  7. Exercise 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.

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    NCERT’s printed answer for this exercise does not match its own question. This working follows the question as printed.

    (a) Solid to vapour with no liquid stage is sublimation.The reverse, vapour to solid, is deposition, not vapourisation; liquid to solid is freezing; solid to liquid is melting, not sublimation.NCERT prints: (b) — a misprint: (b) calls vapour turning to solid "vapourisation," but that change is deposition, leaving (a) as the only true statement.

  8. Exercise 8

    The boiling points of diethyl ether, acetone and n-butyl alcohol are 35\displaystyle 35°C,
    56\displaystyle 56°C and 118\displaystyle 118°C respectively. Which one of the following correctly represents
    their boiling points in kelvin scale?
    (a)
    306\displaystyle 306 K, 329\displaystyle 329 K, 391\displaystyle 391 K
    (b)
    308\displaystyle 308 K, 329\displaystyle 329 K, 392\displaystyle 392 K
    (c)
    308\displaystyle 308 K, 329\displaystyle 329 K, 391\displaystyle 391 K
    (d)
    329\displaystyle 329 K, 392\displaystyle 392 K, 308\displaystyle 308 K

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    NCERT’s answer
    (c)
    (c) $\displaystyle 308$ K, $\displaystyle 329$ K, $\displaystyle 391$ K.\[35\,{}^\circ\text{C} + 273 = 308\text{ K} \] \[56\,{}^\circ\text{C} + 273 = 329\text{ K} \] \[118\,{}^\circ\text{C} + 273 = 391\text{ K} \]

  9. Exercise 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

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    NCERT’s answer
    (a)
    (a) Increase in temperature of water.\[T\uparrow \;\Rightarrow\; KE_{avg}\uparrow \;\Rightarrow\; \text{more molecules cross the surface} \;\Rightarrow\; \text{evaporation}\uparrow \]Lower temperature, a smaller exposed surface, and dissolved salt (which lowers vapour pressure) all slow evaporation instead.

  10. Exercise 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
    (i)
    and (iii)
    (i)
    and (iv)
    (ii)
    and (iii)
    (ii)
    and (iv)
    MATTER IN OUR SURROUNDING S

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    NCERT’s answer
    (c)
    (c) (ii) and (iii).Leaking gas leaves fewer molecules in the same volume; a bigger container spreads them over more space — both raise the average distance. Compressing or adding gas packs molecules closer instead.