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NCERT Exemplar · Class 9 Science Natural Resources

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Multiple Choice Questions 11–20 (part 2 of 6)

  1. Exercise 11

    The term “water-pollution” can be defined in several ways. Which of the
    following statements does not give the correct definition?
    (a)
    The addition of undesirable substances to water-bodies
    (b)
    The removal of desirable substances from water-bodies
    (c)
    A change in pressure of the water bodies
    (d)
    A change in temperature of the water bodies

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    (c)
    (c) A change in pressure of the water bodies.Water pollution means adding undesirable substances, removing desirable ones, or a temperature change that harms water quality; a pressure change is not among these.

  2. Exercise 12

    Which of the following is not a green house gas?
    (a)
    Methane
    (b)
    Carbon dioxide
    (c)
    Carbon monoxide
    (d)
    Ammonia

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    (d)
    (d) Ammonia. \(\displaystyle \text{CH}_4\), \(\displaystyle \text{CO}_2\) and \(\displaystyle \text{CO}\) all count as greenhouse gases (\(\displaystyle \text{CO}\) indirectly, via atmospheric methane and ozone); \(\displaystyle \text{NH}_3\) is washed out of the air within days, so it never accumulates enough to trap heat.

  3. Exercise 13

    Which step is not involved in the carbon-cycle?
    (a)
    Photosynthesis
    (b)
    Transpiration
    (c)
    Respiration
    (d)
    Burning of fossil fuels

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    (b)
    (b) Transpiration. Photosynthesis, respiration and burning of fossil fuels all exchange \(\displaystyle \text{CO}_2\) with the atmosphere; transpiration releases only water vapour and belongs to the water cycle, not the carbon cycle.Answer: (b) Transpiration

  4. Exercise 14

    ‘Ozone-hole’ means
    (a)
    a large sized hole in the ozone layer
    (b)
    thinning of the ozone layer
    (c)
    small holes scattered in the ozone layer
    (d)
    thickening of ozone in the ozone layer

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    (b)
    (b) Thinning of the ozone layer. Ozone concentration over the poles falls sharply each spring but never reaches zero, so the region is thinned, not literally punctured.Answer: (b) Thinning of the ozone layer

  5. Exercise 15

    Ozone-layer is getting depleted because of
    (a)
    excessive use of automobiles
    (b)
    excessive formation of industrial units
    (c)
    excessive use of man-made compounds containing both fluorine and
    chlorine
    (d)
    excessive deforestation.

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    (c)
    (c) Excessive use of man-made compounds containing both fluorine and chlorine. Chlorofluorocarbons release \(\displaystyle \text{Cl}\) atoms in the stratosphere that destroy \(\displaystyle \text{O}_3\) catalytically: \[\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2 \] \[\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2 \] chlorine is regenerated at the end, so one atom destroys many ozone molecules.

  6. Exercise 16

    Which of the following is a recently originated problem of environment?
    (a)
    Ozone layer depletion
    (b)
    Green house effect
    (c)
    Global warming
    (d)
    All of the above

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    (d)
    (d) All of the above. Ozone depletion, the human-enhanced greenhouse effect and the global warming it causes have all emerged in the last few decades from industrial and vehicular emissions.

  7. Exercise 17

    When we breathe in air, nitrogen also goes inside along with oxygen. What
    is the fate of this nitrogen?
    (a)
    It moves along with oxygen into the cells
    (b)
    It comes out with the CO2\displaystyle CO_{2} during exhalation
    (c)
    It is absorbed only by the nasal cells
    (d)
    Nitrogen concentration is already more in the cells so it is not at all
    absorbed.

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    (b)
    (b) It comes out with the \(\displaystyle \text{CO}_2\) during exhalation. Body cells use only oxygen for respiration; nitrogen is chemically inert to them, so there is no net uptake and it leaves unchanged.

  8. Exercise 18

    Top-soil contains the following
    (a)
    Humus and living organisms only
    (b)
    Humus and soil particles only
    (c)
    Humus, living organisms and plants
    (d)
    Humus, living organisms and soil particles.

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    (d)
    (d) Humus, living organisms and soil particles. Plants grow in the top-soil but are not part of the soil itself, unlike the mineral particles, decayed humus and living organisms that make it up.

  9. Exercise 19

    Choose the correct sequences
    (a)
    CO2\displaystyle CO_{2} in atmosphere → decomposers → organic carbon in animals →
    organic carbon in plants
    (b)
    CO2\displaystyle CO_{2} in atmosphere → organic carbon in plants → organic carbon in
    animals → inorganic carbon in soil
    (c)
    Inorganic carbonates in water → organic carbon in plants → organic
    carbon in animals → scavengers
    (d)
    Organic carbon in animals → decomposers → CO2\displaystyle CO_{2} in atmosphere →
    organic carbon in plants

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    (b)
    (b) \(\displaystyle \text{CO}_2\) in atmosphere \(\displaystyle \rightarrow\) organic carbon in plants \(\displaystyle \rightarrow\) organic carbon in animals \(\displaystyle \rightarrow\) inorganic carbon in soil. Plants fix \(\displaystyle \text{CO}_2\) by photosynthesis; animals gain organic carbon by feeding; decomposers return it to the soil as inorganic carbon.

  10. Exercise 20

    Major source of mineral in soil is the
    (a)
    parent rock from which soil is formed
    (b)
    plants
    (c)
    animals
    (d)
    bacteria

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    (a)
    (a) Parent rock from which soil is formed. Weathering breaks the rock into particles that release its minerals; plants, animals and bacteria add only a little mineral matter besides what they recycle.