New NCERT Class 11 Geography Chapter 7: Composition and Structure of Atmosphere Solutions. This chapter explores the envelope of air surrounding our planet, detailing the crucial mix of permanent and variable gases, water vapour, and dust particles. It further breaks down the vertical layers of the atmosphere—from the weather-driven troposphere to the protective ozone-rich stratosphere and beyond. Our detailed solutions help students understand how these atmospheric components sustain life and govern global climate patterns.
(i) 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
- Explanation: Nitrogen accounts for nearly 78% of total atmospheric volume. It is the most abundant gas, followed by oxygen at approximately 21%.
(ii) Atmospheric layer important for human beings is: (a) Stratosphere (b) Mesosphere (c) Troposphere (d) Ionosphere
Answer: (c) Troposphere
- Explanation: The troposphere is the lowermost layer containing water vapour, dust particles, and essential oxygen. All biological activity and weather phenomena occur within this zone.
(iii) 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
Explanation: These solid solid particles originate from oceanic, volcanic, and terrestrial sources. They concentrate in lower atmospheric layers and act as hygroscopic nuclei for cloud formation.
(iv) Question: 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
Explanation: Atmospheric gases thin rapidly with elevation. Oxygen becomes virtually non-existent above 120 km, while carbon dioxide and water vapour extend up to 90 km.
(v) Question: 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
Explanation: Carbon dioxide permits shortwave incoming solar radiation to reach Earth’s surface. It then traps longwave outgoing terrestrial radiation, generating the planetary greenhouse effect.
2. Answer the following questions in about 30 words
(i) What do you understand by atmosphere?
The atmosphere is a huge blanket of air made up of various gases that surrounds the Earth from all sides. It is held in place by the Earth’s gravitational force and contains life-sustaining gases like oxygen for breathing and carbon dioxide for plant photosynthesis. Nearly 99% of its total mass is concentrated within a height of 32 km from the surface.
(ii) What are the elements of weather and climate?
distributional variables that define atmospheric conditions make up the elements of weather and climate. The main elements are:
- Temperature
- Atmospheric pressure
- Winds
- Humidity
- Clouds
- Precipitation
(iii) Describe the composition of atmosphere.
The atmosphere is composed of gases, water vapour, and dust particles:
- Gases: Primarily Nitrogen (78.08%) and Oxygen (20.95%), along with Argon (0.93%), Carbon dioxide (0.03%), and trace gases like Ozone, Helium, and Hydrogen.
- Water Vapour: A variable gas that decreases from the equator toward the poles.
- Dust Particles: Solid particles like sea salt, fine soil, ash, and pollen concentrated in the lower layers.
(iv) Why is troposphere the most important of all the layers of the atmosphere?
The troposphere is the most critical layer because:
- It contains about 75% of the total atmospheric mass, along with almost all the water vapour and dust particles.
- All major weather and climatic phenomena—such as rainfall, fog, cloud formation, and storms—occur exclusively in this layer.
- It directly supports all biological life on Earth.
3. Answer the following questions in about 150 words.
(i) Describe the composition of the atmosphere.
The atmosphere is composed of a mixture of gases, water vapour, and dust particles. Its composition changes dynamically with altitude and location.
- Gases: Permanent gases make up almost the entire atmosphere. Nitrogen (78.08%) and Oxygen (20.95%) are the most abundant. Argon (0.93%) is the primary inert gas. Carbon dioxide (0.03%), though small in quantity, plays a crucial role in absorbing terrestrial radiation, driving the natural greenhouse effect. Ozone, found between 10 to 50 km, absorbs harmful ultraviolet (UV) solar rays.
- Water Vapour: A variable gas that decreases with altitude and from the equator toward the poles. It acts like a blanket, absorbing insolation and preserving radiated heat to regulate Earth’s temperature.
- Dust Particles: Solid matter like sea salt, fine soil, ash, and pollen concentrated in lower layers. They act as hygroscopic nuclei around which water vapour condenses to form clouds and precipitation.
(ii) Draw a suitable diagram for the structure of the atmosphere and label it and describe it.
The atmosphere consists of five distinct thermal layers based on temperature variation and altitude:
- Troposphere: The lowermost layer with an average height of 13 km (8 km at poles, 18 km at equator). Temperature decreases with altitude at a rate of 1.0 degree C per 165 meters (Normal Lapse Rate). All weather phenomena occur here. The Tropopause marks its upper boundary.
- Stratosphere: Extends up to 50 km. It is dry, cloudless, and ideal for flying aircraft. It contains the Ozone layer, which shields life from harmful UV radiation. Its upper limit is the Stratopause.
- Mesosphere: Extends from 50 km to 80 km. Temperature drops with height, reaching up to -100 degree C at the Mesopause. Meteors burn up in this layer.
- Ionosphere (Thermosphere): Located between 80 km and 400 km. It contains electrically charged particles called ions, which reflect radio waves back to Earth for telecommunication.
- Exosphere: The outermost, extremely rarefied layer above 400 km that gradually merges into outer space.