CBSE Class 11 Geography Chapter 8: Composition and Structure of Atmosphere - NCERT Solutions

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This resource provides comprehensive NCERT Solutions for Class 11 Geography, Chapter 8: Composition and Structure of the Atmosphere. It delves into the essential components of our atmosphere, including the major gases like nitrogen and oxygen, the role of water vapor and dust particles, and the distinct layers such as the troposphere and stratosphere. The solutions explain the significance of each atmospheric element and layer, particularly focusing on why the troposphere is vital for human life and weather phenomena. Understanding the composition and structure is crucial for grasping concepts related to weather, climate, and the Earth's environmental systems. These solutions are designed to aid students in clarifying doubts and preparing effectively for their examinations by offering clear, concise explanations.

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BoardCBSE
ClassClass 11
SubjectGeography
Session2026
LanguageEnglish
TypeNCERT Solutions
Chapter8. Composition and Structure of Atmosphere

Chapter summary

This chapter focuses on the fundamental composition and structural layers of the Earth's atmosphere. It details the gases present, the significance of water vapor and dust particles, and the distinct characteristics of atmospheric layers like the troposphere and stratosphere. The solutions explain the importance of the troposphere for weather and life, and the role of gases like carbon dioxide in radiation balance. This section is key for understanding atmospheric processes and their impact on climate.

Learning outcomes

  • Understand the primary gases that constitute the Earth's atmosphere.
  • Identify the role of water vapor and dust particles in atmospheric composition.
  • Explain the importance of different atmospheric layers, especially the troposphere.
  • Describe the process by which certain gases interact with solar and terrestrial radiation.
  • Recognize the factors influencing weather and climate.

Topics covered

Paper topics

  • Atmosphere composition
  • Major atmospheric gases
  • Nitrogen
  • Oxygen
  • Carbon dioxide
  • Water vapor
  • Dust particles
  • Atmospheric layers
  • Troposphere
  • Stratosphere
  • Weather elements
  • Radiation balance

Important topics

  • Composition of the atmosphere (gases, water vapor, dust)
  • Importance of the Troposphere
  • Role of Carbon Dioxide in radiation
  • Vertical structure of the atmosphere
  • Elements of weather and climate

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Questions and Solutions

Question 1

Which one of the following gases constitutes the major portion of the atmosphere?
  1. Oxygen
  2. Nitrogen
  3. Argon
  4. Carbon dioxide
Solution: The Earth's atmosphere is a mixture of gases. The gas that makes up the largest proportion is Nitrogen. It accounts for approximately 78% of the dry air. Oxygen is the second most abundant gas at about 21%, followed by Argon (about 0.93%) and Carbon Dioxide (about 0.04%), with trace amounts of other gases. Therefore, Nitrogen constitutes the major portion.

Answer: (b) Nitrogen

Question 2

Which atmospheric layer is important for human beings?
  1. Stratosphere
  2. Mesosphere
  3. Troposphere
  4. Ionosphere
Solution: The troposphere is the lowest layer of the Earth's atmosphere, extending from the surface up to an average altitude of about 12 km. This layer is crucial for human beings because it contains most of the atmosphere's mass, including the air we breathe (oxygen), water vapor, and dust particles. All significant weather phenomena, such as rain, snow, storms, and temperature variations, occur within the troposphere, making it the most vital layer for life on Earth.

Answer: (c) Troposphere

Question 3

Sea salt, pollen, ash, smoke soot, fine soil — these are associated with:
  1. Gases
  2. Dust particles
  3. Water vapour
  4. Meteors
Solution: The items listed – sea salt, pollen, ash, smoke soot, and fine soil – are all examples of solid particles that are suspended in the Earth's atmosphere. These particles, along with others like volcanic ash and industrial pollutants, are collectively referred to as dust particles or aerosols. They play a role in scattering sunlight, forming cloud condensation nuclei, and influencing air quality.

Answer: (b) Dust particles

Question 4

Oxygen gas is in negligible quantity at the height of atmosphere:
  1. 90 km
  2. 120 km
  3. 100 km
  4. 150 km
Solution: The concentration of gases in the atmosphere decreases significantly with increasing altitude. While oxygen is abundant in the lower layers like the troposphere and stratosphere, its proportion diminishes rapidly at higher altitudes. By the time one reaches an altitude of approximately 120 km, the amount of oxygen becomes extremely small, considered negligible for breathing purposes and most atmospheric processes.

Answer: (b) 120 km

Question 5

Which one of the following gases is transparent to incoming solar radiation and opaque to outgoing terrestrial radiation?
  1. Oxygen
  2. Nitrogen
  3. Helium
  4. Carbon dioxide
Solution: Carbon dioxide (CO2) is a significant greenhouse gas. It allows most of the incoming shortwave solar radiation to pass through the atmosphere and reach the Earth's surface. However, it is largely opaque to the outgoing longwave terrestrial radiation emitted by the Earth. CO2 absorbs this outgoing radiation and re-emits it in all directions, including back towards the Earth's surface, trapping heat and contributing to the warming of the planet. Other gases like water vapor also exhibit this property.

Answer: (d) Carbon dioxide

Question 6

What do you understand by atmosphere?
Solution: The atmosphere is the layer of gases that surrounds the Earth, held in place by gravity. It is a vital envelope that protects life on Earth. It is composed of a mixture of gases, primarily nitrogen and oxygen, along with smaller amounts of argon, carbon dioxide, and trace gases. The atmosphere also contains water vapor and suspended particles. It provides the air necessary for respiration for humans and animals and the carbon dioxide required by plants for photosynthesis.

Question 7

What are the elements of weather and climate?
Solution: Weather and climate are described and measured using several key elements. These include temperature, which measures heat intensity; atmospheric pressure, the weight of the air; winds, the movement of air; humidity, the amount of water vapor in the air; cloud cover, the extent of the sky obscured by clouds; and precipitation, which refers to any form of water falling from the atmosphere, such as rain, snow, or hail.

Question 8

Describe the composition of atmosphere.
Solution: The Earth's atmosphere is a complex mixture comprising several components. The most significant are gases, with nitrogen (about 78%) and oxygen (about 21%) making up the vast majority of dry air. Other gases present in smaller, but important, quantities include argon (0.93%), carbon dioxide (around 0.04%), and trace amounts of neon, helium, krypton, hydrogen, and ozone. Besides these gases, the atmosphere also contains variable amounts of water vapor, which is crucial for weather and climate, and various suspended solid and liquid particles, known as dust particles or aerosols.

Question 9

Why is troposphere the most important of all the layers of the atmosphere?
Solution: The troposphere holds the greatest importance for human beings and most life forms on Earth. It is the lowest layer of the atmosphere, extending from the Earth's surface up to an average height of about 12 kilometers. This layer contains nearly all of the atmosphere's water vapor and about three-quarters of its mass. Crucially, all the weather phenomena we experience – such as clouds, rain, snow, storms, and temperature fluctuations – occur within the troposphere. The presence of breathable air (oxygen) and water vapor makes it the zone where life thrives and atmospheric processes are most dynamic.

Question 10

Describe the composition of the atmosphere.
Solution: The atmosphere is composed of a variety of elements, primarily gases, water vapor, and dust particles. The gaseous component is dominated by nitrogen (approximately 78%) and oxygen (approximately 21%), with smaller but significant amounts of argon (about 0.93%) and carbon dioxide (about 0.04%). Trace gases like neon, helium, and ozone are also present. Water vapor content varies significantly by location and altitude but is essential for weather. Additionally, the atmosphere contains suspended solid and liquid particles, such as sea salt, pollen, ash, and soot, which influence atmospheric processes like cloud formation and radiation scattering.

Common mistakes

  • Confusing the primary gas component of the atmosphere.
  • Underestimating the importance of the troposphere for life and weather.
  • Not understanding the selective transparency of gases to radiation.
  • Misidentifying the height at which oxygen becomes negligible.

Revision tips

  • Memorize the percentage composition of major atmospheric gases.
  • Focus on the unique characteristics and importance of each atmospheric layer.
  • Understand the role of greenhouse gases like carbon dioxide in regulating Earth's temperature.
  • Review the elements that define weather and climate.

Practice MCQs

Q1. Which gas forms the largest proportion of the Earth's atmosphere?

Q2. The atmospheric layer most crucial for human existence and weather phenomena is:

Q3. What atmospheric components are represented by sea salt, pollen, ash, and smoke soot?

Q4. At approximately what altitude does oxygen become virtually absent in the atmosphere?

Q5. Which gas is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation, contributing to the greenhouse effect?

Frequently asked questions

What is the atmosphere?

The atmosphere is a blanket of various gases surrounding the Earth, containing essential elements like oxygen for respiration and carbon dioxide for plant photosynthesis.

What are the main components of the atmosphere?

The atmosphere is primarily composed of gases (like nitrogen and oxygen), water vapor, and suspended dust particles.

Why is the troposphere considered the most important layer of the atmosphere?

The troposphere is the lowest layer where all weather phenomena occur, and it contains the water vapor and dust necessary for life and atmospheric processes.

Which gas is key to regulating Earth's temperature by trapping outgoing radiation?

Carbon dioxide is crucial because it is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation, thus contributing to the greenhouse effect.

At what height does oxygen become negligible in the atmosphere?

Oxygen concentration significantly decreases with altitude and becomes negligible at approximately 120 km.

What are the basic elements that define weather and climate?

The main elements include temperature, atmospheric pressure, wind, humidity, cloud cover, and precipitation.

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