NCERT Class 11 Geography — Chapter 1: Composition and Structure of Atmosphere

mcqeasy

Which of the following is a variable gas in the atmosphere?

Official previous-year question

Verified 1 Aug 2026.

Options

ANitrogen
BArgon
COxygen
DWater Vapour

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Solution

The correct option is Water Vapour.

Explanation

The gases in the atmosphere are broadly classified into two categories based on the stability of their concentration:

Permanent Gases: These gases maintain a constant proportion in the lower atmosphere. Examples include Nitrogen, Oxygen, and Argon.
Variable Gases: The concentration of these gases changes with time and place. Examples include Water Vapour, Carbon Dioxide, and Ozone.

Option Analysis

Nitrogen Nitrogen: Incorrect. Nitrogen is the most abundant gas in the atmosphere, constituting approximately 78.08% by volume. It is a permanent gas with a fixed proportion.
Oxygen Oxygen: Incorrect. Oxygen constitutes approximately 20.95% of the atmosphere by volume. It is a permanent gas essential for combustion and respiration.
Water Vapour Water Vapour: Correct. Water vapour is a highly variable gas. Its volume in the atmosphere varies from zero to four %. It decreases from the equator towards the poles and absorbs parts of the insolation from the sun, acting like a blanket for the earth.
Argon Argon: Incorrect. Argon is an inert, permanent gas constituting approximately 0.93% of the atmosphere.

Key Takeaway

Water Vapour is the most significant variable gas in the atmosphere, with concentrations ranging from nearly 0% in dry, cold regions to about 4% in warm, humid tropics.

Your note

More from Chapter 1: Composition and Structure of Atmosphere

Consider the following statements regarding the composition of the atmosphere: 1. The proportion of gases remains constant up to the highest layers of the atmosphere. 2. Nitrogen is the most abundant gas in the atmosphere. 3. Nitrogen and Oxygen make up the bulk of the atmosphere. Which of the statements given above is/are correct?

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Which of the following is the main reason for the rising volume of carbon dioxide in the atmosphere?

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Consider the following statements regarding water vapour in the atmosphere: 1. It is a variable gas that increases with altitude. 2. It accounts for less than one % of the air by volume in the dry and cold polar regions. 3. It absorbs parts of the insolation from the sun and preserves the earth’s radiated heat. Which of the statements given above is/are correct?

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With reference to the composition of the atmosphere, consider the following statements: 1. Oxygen is found in substantial quantities at heights above 120 km from the earth's surface. 2. Carbon dioxide is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation. 3. Carbon dioxide and water vapour are found in uniform concentration up to the exosphere. Which of the statements given above is/are correct?

medium

Which one of the following is the most likely reason for the higher concentration of dust particles in subtropical and temperate regions compared to equatorial regions?

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The correct option is Water Vapour.

Explanation

The gases in the atmosphere are broadly classified into two categories based on the stability of their concentration:

Permanent Gases: These gases maintain a constant proportion in the lower atmosphere. Examples include Nitrogen, Oxygen, and Argon.
Variable Gases: The concentration of these gases changes with time and place. Examples include Water Vapour, Carbon Dioxide, and Ozone.

Option Analysis

Nitrogen Nitrogen: Incorrect. Nitrogen is the most abundant gas in the atmosphere, constituting approximately 78.08% by volume. It is a permanent gas with a fixed proportion.
Oxygen Oxygen: Incorrect. Oxygen constitutes approximately 20.95% of the atmosphere by volume. It is a permanent gas essential for combustion and respiration.
Water Vapour Water Vapour: Correct. Water vapour is a highly variable gas. Its volume in the atmosphere varies from zero to four %. It decreases from the equator towards the poles and absorbs parts of the insolation from the sun, acting like a blanket for the earth.
Argon Argon: Incorrect. Argon is an inert, permanent gas constituting approximately 0.93% of the atmosphere.

Key Takeaway

Water Vapour is the most significant variable gas in the atmosphere, with concentrations ranging from nearly 0% in dry, cold regions to about 4% in warm, humid tropics.