Class 9 Composition and Structure of the Atmosphere Mock Test (ICSE)

Topics in Composition and Structure of the Atmosphere

• Composition of the atmosphere
• Layers of the atmosphere
• Ozone depletion
• Global warming

Composition and Structure of the Atmosphere practice questions with answers

1. Q1Multiple choice·1 mark
   In which layer of the atmosphere does temperature decrease with an increase in altitude, and where all major weather phenomena occur?

   1. (a)Mesosphere
   2. (b)Troposphere
   3. (c)Thermosphere
   4. (d)Stratosphere
   Show answer and step marks

   1. Correct option: (b) Troposphere. It is the lowest layer, where temperature falls with height and clouds, rain and storms occur.+1

   Answer: (b)
2. Q2Multiple choice·1 mark
   Which of the following greenhouse gases is primarily emitted through human activities and contributes most significantly to global warming?

   1. (a)Neon ($\text{Ne}$)
   2. (b)Argon ($\text{Ar}$)
   3. (c)Carbon dioxide ($\text{CO}_2$)
   4. (d)Helium ($\text{He}$)
   Show answer and step marks

   1. Correct option: (c) Carbon dioxide ($\text{CO}_2$)+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   Which of the following components of the atmosphere is classified as a variable gas and plays a crucial role in absorbing terrestrial radiation and driving weather phenomena?

   1. (a)Neon
   2. (b)Argon
   3. (c)Water vapour
   4. (d)Helium
   Show answer and step marks

   1. Correct option: (c) Water vapour+1

   Answer: (c)
4. Q4Multiple choice·1 mark
   Which chemical compound is primarily responsible for the depletion of the ozone layer in the stratosphere?

   1. (a)Chlorofluorocarbons ($\text{CFCs}$)
   2. (b)Sulphur dioxide ($\text{SO}_2$)
   3. (c)Carbon monoxide ($\text{CO}$)
   4. (d)Methane ($\text{CH}_4$)
   Show answer and step marks

   1. Correct option: (a) Chlorofluorocarbons ($\text{CFCs}$)+1

   Answer: (a)
5. Q5Long answer·4 marks
   State the approximate percentage by volume of the two major permanent gases found in the atmosphere. Explain one specific significance of each gas to life on Earth.
   Show answer and step marks

   1. Nitrogen constitutes about $78\%$ of the atmosphere by volume.+0.5
   2. Oxygen constitutes about $21\%$ of the atmosphere by volume.+0.5
   3. Significance of nitrogen, any one of: it dilutes oxygen and so controls the rate of burning; it is fixed by bacteria and lightning into compounds that plants need to make proteins; or any other valid significance.+1.5
   4. Significance of oxygen, any one of: it is needed for respiration by humans, animals and most living organisms; it is needed for burning (combustion) of fuels; it forms the ozone layer that absorbs harmful ultraviolet rays; or any other valid significance.+1.5

   Answer: Nitrogen about $78\%$ (dilutes oxygen to control burning, or supplies plants with nitrogen for proteins) and oxygen about $21\%$ (needed for respiration, or for combustion).

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