Important Questions and Answers for Class 11 Geography Chapter 7 Composition and Structure of Atmosphere 2025-26

Q1. Which one of the following gases constitutes the major portion of the atmosphere?

• (a) Oxygen
• (b) Nitrogen
• (c) Argon
• (d) Carbon dioxide

Answer: (b) Nitrogen. 

Nitrogen forms about 78% of the earth's atmosphere, making it the most abundant gas present.

Q2. Which atmospheric layer is most important for human beings?

• (a) Stratosphere
• (b) Mesosphere
• (c) Troposphere
• (d) Ionosphere

Answer: (c) Troposphere. 

The troposphere contains air, water vapor, and is where all weather phenomena occur, which support life on earth.

Q3. Sea salt, pollen, ash, smoke soot, fine soil — these are associated with:

• (a) Gases
• (b) Dust particles
• (c) Water vapour
• (d) Meteors

Answer: (b) Dust particles. 

These items are examples of solid particles in the atmosphere, which help in cloud formation.

Q4. Oxygen gas is in negligible quantity at the height of atmosphere:

• (a) 90 km
• (b) 120 km
• (c) 100 km
• (d) 150 km

Answer: (b) 120 km. 

At this height, oxygen is almost negligible compared to lower atmospheric levels.

Q5. Which one of the following gases is transparent to incoming solar radiation and opaque to outgoing terrestrial radiation?

• (a) Oxygen
• (b) Nitrogen
• (c) Helium
• (d) Carbon dioxide

Answer: (d) Carbon dioxide. 

CO₂ is transparent to incoming sunlight but traps heat, causing the greenhouse effect.

2. Very Short Answer (VSA).

Q6. Define atmosphere.

Answer: Atmosphere is a mixture of different gases that envelops the earth, containing life-giving gases like oxygen and carbon dioxide, and is essential for sustaining life.

Q7. Name any two elements of weather and climate.

Answer: Two main elements of weather and climate are temperature and pressure. These elements constantly change and directly influence weather conditions.

Q8. What is the main role of ozone in the atmosphere?

Answer: Ozone layer filters and absorbs harmful ultraviolet rays from the sun, providing a shield that protects life on earth from UV radiation.

Q9. What is the characteristic feature of the troposphere?

Answer: The troposphere is the lowest layer, containing most of the atmospheric mass, dust, and water vapor, where all weather and climate changes happen.

3. Short Answer Questions.

Q10. Describe any two factors that control the temperature of the atmosphere.

Answer: The two main factors are altitude and latitude. With increase in altitude, temperature decreases as density decreases. Latitude affects the angle of incidence of sun’s rays, influencing how much solar energy a place receives and thus its temperature.

Q11. What is the role of dust and salt particles in atmospheric phenomena?

Answer: Dust and salt particles act as condensation nuclei in the atmosphere. Water vapor condenses around these particles to form clouds and precipitation, affecting weather patterns, especially in subtropical and temperate regions.

Q12. Explain why the stratosphere is crucial for the earth's survival.

Answer: The stratosphere houses the ozone layer, which absorbs harmful ultraviolet radiation. Without it, living organisms would be exposed to dangerous UV rays, impacting health and ecosystem stability.

4. Long Answer Questions.

Q13. Explain the composition of the atmosphere and its significance for life on earth.

Answer: The atmosphere is made up primarily of nitrogen (about 78%) and oxygen (about 21%), with minor gases like argon, carbon dioxide, and variable amounts of water vapor and dust particles. Nitrogen supports plant growth, oxygen is vital for respiration, and carbon dioxide is utilized by plants and is key for the greenhouse effect. Water vapor regulates temperature and causes precipitation. Dust particles help cloud formation. This composition maintains earth’s temperature, supports weather, and enables the existence of life.

1. Nitrogen and oxygen form the bulk of the air.
2. Minor gases contribute to climate stability.
3. Water vapor regulates heat and enables rain.

Q14. Analyse the structure of the atmosphere highlighting each layer’s features.

Answer: The atmosphere consists of several layers, each with distinct features. The troposphere is closest to earth, contains weather and dust, and shows rapid temperature decline with altitude. The stratosphere above it contains ozone and stable temperatures. Mesosphere sees temperature decreasing and meteors burning up. The ionosphere (part of thermosphere) has ions reflecting radio waves and higher temperatures. The exosphere is the outermost, merging with space. Each layer plays unique roles supporting life, communication, or protection.

1. Troposphere: weather, biological activity.
2. Stratosphere: ozone absorption, calm.
3. Mesosphere: temperature drops, meteors.
4. Ionosphere: charged particles, radio signals.
5. Exosphere: sparse, merges with outer space.

Q15. Evaluate how the greenhouse effect impacts global climate.

Answer: The greenhouse effect is mainly caused by gases like carbon dioxide that trap outgoing terrestrial radiation. While this effect keeps earth’s temperature suitable for life, excessive greenhouse gases lead to global warming and climate change. This disrupts weather patterns, increases sea levels, and affects ecosystems globally.

5. Assertion–Reason type questions.

Assertion (A): The troposphere is the most important atmospheric layer for biological activity.
Reason (R): All significant weather changes and phenomena occur in this layer.

• (a) A and R are true, and R is the correct explanation of A
• (b) A and R are true, but R is not the correct explanation of A
• (c) A is true, but R is false
• (d) A is false, but R is true

Answer: (a) Both statements are true, and the reason correctly explains why the troposphere is crucial for biological activity.

Assertion (A): The concentration of dust particles is highest in subtropical and temperate regions.
Reason (R): Equatorial and polar regions have more dry winds than subtropical regions.

• (a) A and R are true, and R is the correct explanation of A
• (b) A and R are true, but R is not the correct explanation of A
• (c) A is true, but R is false
• (d) A is false, but R is true

Answer: (c) Assertion is true as dry winds in subtropical/temperate areas raise more dust; Reason is false since subtropical regions, not equatorial or polar, have more dry winds.

3. Fill in the Blanks Questions.

Q16. The layer of the atmosphere that contains the ozone layer and absorbs ultraviolet radiation is called the ________.

Answer: Stratosphere. 

The stratosphere houses the ozone layer, which plays a vital role in protecting living organisms by filtering harmful ultraviolet rays from the sun.

Q17. The temperature in the troposphere decreases at the rate of ________ for every 165 m of height.

Answer: 1°C. 

With every 165 meters of ascent in the troposphere, the temperature typically drops by about 1°C due to decreasing air density.

Why Understanding the Composition and Structure of Atmosphere Matters?

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