Atmosphere: Composition & Structure – NDA Geography PYQs

Question 1 [NDA 2007-II]
Injurious ultraviolet radiations are mostly prevented from reaching the land surface as these are absorbed mostly by which one of the following?
(a) Stratosphere
(b) Troposphere
(c) Ionosphere
(d) Mesosphere

Answer: (a) Stratosphere
The ozone layer, located within the stratosphere between 15 and 35 km altitude, absorbs most of the Sun’s harmful ultraviolet radiation. The troposphere is the lowest layer where weather occurs. The ionosphere reflects radio waves. The mesosphere is where meteors burn up.

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Question 2 [NDA 2009-II]
Which one of the following is the correct order in which the gases from the atmosphere disappear as one moves away from the surface of the Earth?
(a) Carbon dioxide – Oxygen – Nitrogen
(b) Oxygen – Nitrogen – Carbon dioxide
(c) Carbon dioxide – Nitrogen – Oxygen
(d) Nitrogen – Oxygen – Carbon dioxide

Answer: (a) Carbon dioxide – Oxygen – Nitrogen
Carbon dioxide is the heaviest of these three and stays closest to the surface — it decreases first. Oxygen extends higher. Nitrogen is the lightest of the three and extends highest before becoming negligible. The sequence in which they disappear going upward is CO₂ → O₂ → N₂.

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Question 3 [NDA 2013-II]
It is known that the atmosphere is divided into some layers. In which one among the following layers is the percentage composition of Helium gas maximum?
(a) Troposphere
(b) Stratosphere
(c) Exosphere
(d) Ionosphere

Answer: (c) Exosphere
In the exosphere — the outermost layer — the very lightest gases (hydrogen and helium) dominate because heavier gases cannot reach these extreme altitudes. Hydrogen is the most abundant gas in the exosphere, followed by helium.

Question 4 [NDA 2013-II]
Consider the following layers of the atmosphere:

1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere

Which one among the following is the correct sequence of the layers with increasing altitude from the Earth’s surface?
(a) 1-2-3-4
(b) 2-1-3-4
(c) 3-2-1-4
(d) 4-2-3-1

Answer: (a) 1-2-3-4
From the surface upward: Troposphere (1) → Stratosphere (2) → Mesosphere (3) → Thermosphere (4) → Exosphere. This sequence must be memorised exactly — NDA tests it in multiple papers.

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Question 5 [NDA 2013-II]
Which one among the following atmospheric gases filters out most of the ultraviolet radiation of the Sun?
(a) Oxygen
(b) Nitrogen
(c) Helium
(d) Ozone

Answer: (d) Ozone
Ozone (O₃) in the stratosphere absorbs the vast majority of the Sun’s ultraviolet radiation. Oxygen does absorb some UV in the upper atmosphere, but ozone is far more effective. Nitrogen and Helium do not significantly absorb UV radiation.

Question 6 [NDA 2014-I]
Statement I: The decrease of air temperature with increasing altitudes in the atmosphere is called the vertical temperature gradient.
Statement II: In Troposphere, air temperature decreases with increasing altitude due to radiation from the Earth.

(a) Both true and II explains I
(b) Both true but II does not explain I
(c) I true but II false
(d) I false but II true

Answer: (a) Both true and II explains I
The vertical temperature gradient (lapse rate) in the troposphere is indeed a decrease of temperature with altitude. This happens because the troposphere is heated from below by terrestrial (long-wave) radiation from the Earth’s surface. As you move up and away from this heat source, temperature drops. Statement II correctly explains why Statement I is true.

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Question 7 [NDA 2015-II]
Which one of the following gases is found in highest quantity in the Exosphere?
(a) Hydrogen
(b) Helium
(c) Nitrogen
(d) Oxygen

Answer: (a) Hydrogen
Hydrogen is the lightest of all elements and is found in the highest quantities in the exosphere. Only the very lightest gases — hydrogen and helium — can reach these extreme altitudes. Nitrogen and oxygen, being heavier, are concentrated much lower in the atmosphere.

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Question 8 [NDA 2016-II]
Statement I: Ozone is a tri-atomic molecule of oxygen.
Statement II: Ozone is concentrated mainly in stratosphere.

(a) Both true and II is correct explanation of I
(b) Both true but II is not explanation of I
(c) I true but II false
(d) I false but II true

Answer: (a) Both true and II is correct explanation of I
Ozone (O₃) does contain three oxygen atoms — making it a tri-atomic molecule. It is concentrated mainly in the stratosphere where it forms the protective ozone layer. Statement II provides context that explains the significance of ozone being tri-atomic — its presence in the stratosphere enables it to absorb UV radiation.

Question 9 [NDA 2017-II]
Which one of the following gases is placed second in respect of abundance in the Earth’s atmosphere?
(a) Oxygen
(b) Hydrogen
(c) Nitrogen
(d) Carbon dioxide

Answer: (a) Oxygen
Nitrogen is the most abundant gas in the atmosphere at about 78%. Oxygen is second at about 21%. Argon is third at about 0.93%. Carbon dioxide is fourth at about 0.04%. Hydrogen is present in only trace amounts in the lower atmosphere.

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Question 10 [NDA 2018-II]
Which one of the following statements about temperature is correct?
(a) Temperature decreases with height in the stratosphere
(b) Temperature is constant at different heights in the stratosphere
(c) Temperature increases with height in the troposphere at an average rate of 6.5°C per kilometre
(d) Temperature decreases with height in the troposphere at an average rate of 6.4°C per kilometre

Answer: (d) Temperature decreases with height in the troposphere at an average rate of 6.4°C per kilometre
Option (a) is wrong — temperature increases in the stratosphere. Option (b) is wrong — temperature is not constant; it increases. Option (c) is wrong — temperature decreases in the troposphere (not increases). Option (d) is correct — temperature decreases in the troposphere at approximately 6.4°C per kilometre.

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Question 11 [NDA 2019-II]
The normal lapse rate of temperature of Earth’s atmosphere drops to 0°C at the:
(a) Upper part of ionosphere
(b) Upper boundary of the tropopause
(c) Lower part of mesosphere
(d) Upper boundary of stratopause

Answer: (b) Upper boundary of the tropopause
The environmental lapse rate (decrease of temperature with altitude) reaches its minimum at the tropopause — the top of the troposphere. At the tropopause, temperature stops decreasing and becomes roughly constant (around −57°C average). This is the boundary between the troposphere and the stratosphere.

Question 12 [NDA 2023-II]
In which one of the following layers of the atmosphere do all weather phenomena occur?
(a) Mesosphere
(b) Troposphere
(c) Thermosphere
(d) Stratosphere

Answer: (b) Troposphere
All clouds, rain, snow, cyclones, thunderstorms, and other weather phenomena occur in the troposphere — the lowest layer of the atmosphere. This layer contains most of the atmosphere’s water vapour and is heated from the surface below, creating the convection and instability that drives weather.

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Question 13 [NDA 2024-I]
Which of the following statements regarding aurora is/are correct?

1. The solar wind upon reaching the Earth’s atmosphere is directed toward the two magnetic poles and a colourful display of lights is seen in the night sky.
2. The particles interact with the different gases of the atmosphere and each gas glows with a particular colour.
3. In April 2023, aurora was captured in the night sky in India by the Indian Astronomical Observatory at Hanle, Ladakh.

(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Answer: (d) 1, 2 and 3
All three statements are correct. Solar wind particles are directed toward the magnetic poles where they enter the atmosphere. Different gases produce different colours — oxygen makes green and red auroras, nitrogen makes blue and purple. The 2023 aurora visible from Ladakh was a notable event captured by the Indian Astronomical Observatory.

Question 14 [NDA 2025-II]
Consider the following statements with reference to structure of the Earth’s atmosphere:

1. Thickness of the troposphere is greatest at the equator.
2. The air temperature of the tropopause is highest above the poles.
3. The temperature in troposphere decreases at the rate of 1°F for every 165 m of height.

Which of the statements given above is/are correct?
(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2 and 3

Answer: (a) 1 only
Statement 1 is correct — the troposphere is thickest at the equator (about 16 km) because warm air expands upward more in the tropics. Statement 2 is wrong — the tropopause temperature is actually coldest above the tropics (not highest above the poles). Statement 3 needs checking — 1°F per 165 m converts to approximately 3.3°C per 300 m = 11°C per km which is too high. The standard metric lapse rate is 6.4°C per km. This statement appears to contain a conversion error — however the PYQ answer given is (a) 1 only, confirming only Statement 1 is correct.

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Practice Question 1 (Important for NDA)
Consider the following statements related to stratification of atmospheric layers:

1. All storms and cloudiness are restricted to the stratosphere.
2. Cirrus clouds are formed on the top layers of the troposphere.
3. Stratosphere is also an isoclinal layer.

Which of the statements given above are correct?
(a) 1 and 2
(b) 1 and 3
(c) 2 and 3
(d) 1, 2 and 3

Answer: (c) 2 and 3
Statement 1 is wrong — all storms and cloudiness occur in the TROPOSPHERE, not the stratosphere. Statement 2 is correct — cirrus clouds are the highest-altitude clouds and form at the very top of the troposphere (9–12 km). Statement 3 is correct — the stratosphere is indeed called an isoclinal layer because it has a nearly uniform temperature gradient.