Consider the following statements regarding the vertical distribution of gases: 1. Oxygen is almost negligible at heights above 120 km. 2. Carbon dioxide is found in abundance up to 500 km. 3. Water vapour is found uniformly throughout the atmosphere. Which of the statements given above is/are correct?

The correct option is 1 only Explanation The atmosphere is a mixture of gases, water vapour, and dust particles. However, the composition of the atmosphere is not uniform vertically. The density of gases is highest near the Earth's surface and decreases with increasing altitude. Heavier gases are concentrated in the lower layers, while lighter gases dominate the upper layers. Statement-wise Analysis: - Statement 1 is Correct: Oxygen is a relatively heavy gas compared to hydrogen or helium. Due to gravitational separation and the structure of the atmosphere, the concentration of oxygen becomes almost negligible at heights above 120 km. - Statement 2 is Incorrect: Carbon dioxide is a heavy gas and is largely concentrated in the lower atmosphere. It is found in significant quantities only up to a height of 90 km from the surface of the Earth, not 500 km. - Statement 3 is Incorrect: Water vapour is not distributed uniformly throughout the atmosphere. It is highly variable and decreases rapidly with altitude. Like carbon dioxide, water vapour is found effectively only up to a height of 90 km. Furthermore, it decreases from the equator towards the poles. Key Takeaway: Carbon dioxide and water vapour are found only up to 90 km, while oxygen becomes negligible above 120 km. The upper atmosphere is dominated by lighter gases like helium and hydrogen.

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

mcqmedium

Consider the following statements regarding the vertical distribution of gases:

Oxygen is almost negligible at heights above 120 km.
Carbon dioxide is found in abundance up to 500 km.
Water vapour is found uniformly throughout the atmosphere.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

A1 and 3 only
B1 only
C2 only
D1, 2 and 3

Did you get this right?

Solution

The correct option is

1 only

Explanation

The atmosphere is a mixture of gases, water vapour, and dust particles. However, the composition of the atmosphere is not uniform vertically. The density of gases is highest near the Earth's surface and decreases with increasing altitude. Heavier gases are concentrated in the lower layers, while lighter gases dominate the upper layers.

Statement-wise Analysis:

Statement 1 is Correct: Oxygen is a relatively heavy gas compared to hydrogen or helium. Due to gravitational separation and the structure of the atmosphere, the concentration of oxygen becomes almost negligible at heights above 120 km.
Statement 2 is Incorrect: Carbon dioxide is a heavy gas and is largely concentrated in the lower atmosphere. It is found in significant quantities only up to a height of 90 km from the surface of the Earth, not 500 km.
Statement 3 is Incorrect: Water vapour is not distributed uniformly throughout the atmosphere. It is highly variable and decreases rapidly with altitude. Like carbon dioxide, water vapour is found effectively only up to a height of 90 km. Furthermore, it decreases from the equator towards the poles.

Key Takeaway:

Carbon dioxide and water vapour are found only up to 90 km, while oxygen becomes negligible above 120 km. The upper atmosphere is dominated by lighter gases like helium and hydrogen.

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?

easy

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

easy

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?

medium

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?

easy

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The correct option is

1 only

Explanation

Statement-wise Analysis:

Statement 1 is Correct: Oxygen is a relatively heavy gas compared to hydrogen or helium. Due to gravitational separation and the structure of the atmosphere, the concentration of oxygen becomes almost negligible at heights above 120 km.
Statement 2 is Incorrect: Carbon dioxide is a heavy gas and is largely concentrated in the lower atmosphere. It is found in significant quantities only up to a height of 90 km from the surface of the Earth, not 500 km.
Statement 3 is Incorrect: Water vapour is not distributed uniformly throughout the atmosphere. It is highly variable and decreases rapidly with altitude. Like carbon dioxide, water vapour is found effectively only up to a height of 90 km. Furthermore, it decreases from the equator towards the poles.

Key Takeaway:

Carbon dioxide and water vapour are found only up to 90 km, while oxygen becomes negligible above 120 km. The upper atmosphere is dominated by lighter gases like helium and hydrogen.