Composition and Structure of the Atmosphere: ICSE Class 9 Geo

Summary

The Earth is surrounded by a layer of air called the atmosphere. Think of it as a large, invisible blanket. This air has several layers and gets thinner higher up, making breathing difficult on high mountains. Gravity keeps this air close. The atmosphere is mostly nitrogen and oxygen. Oxygen is for breathing and burning. Nitrogen is also vital for life. A small part includes carbon dioxide, used by plants, and water vapour, which forms clouds and rain.

This air blanket has important jobs. It protects us from some harmful sun rays. It keeps Earth warm enough for life. It also helps move water, giving us rain. The atmosphere has layers. The lowest is the troposphere, where we live. Most air and all weather, like clouds and storms, are here. Temperature in the troposphere drops with height.

Above the troposphere is the stratosphere. It has the ozone layer, which absorbs most of the sun’s harmful ultraviolet rays. This layer is calm, good for jet planes. Higher still are the mesosphere and thermosphere. The thermosphere includes the ionosphere, with charged particles creating auroras and helping radio signals. The exosphere is the top layer, fading into space.

The ozone layer can be damaged. Human-made chemicals can destroy ozone, creating thin spots or “ozone holes.” This allows more harmful sun rays to reach Earth.

Global warming means Earth is slowly getting warmer. This is due to the greenhouse effect. Some gases, like carbon dioxide, act like glass in a greenhouse. A greenhouse lets sunlight in but traps heat inside. These “greenhouse gases” trap Earth’s heat. Burning fuels and cutting forests add more of these gases, trapping more heat.

This warming causes changes. Melting ice makes sea levels rise, affecting coastal areas. Weather patterns can shift, causing floods or droughts. It impacts farming and water. Taking care of our atmosphere helps keep Earth healthy.

Textbook solutions (Morning Star/Total)

Multiple-Choice Questions

1. The blanket of air surrounding the earth is known as the:

(a) Ozone layer
(b) Nitrogen layer
(c) Lithosphere
(d) Atmosphere

Answer: (d) Atmosphere

2. A clean dry sample of air is made up of _______ percent nitrogen:

(a) 72
(b) 77
(c) 78
(d) 79

Answer: (c) 78

3. About 90 percent of air mass lies within about _______ from the earth’s surface.

(a) 20 km
(b) 22 km
(c) 25 km
(d) 30 km

Answer: (a) 20 km

4. Name the densest layer of the atmosphere.

(a) Exosphere
(b) Troposphere
(c) Stratosphere
(d) Mesosphere

Answer: (b) Troposphere

5. Mountain climbers set up camps at the base as well as at regular intervals along their climb. Why?

(a) To acclimatize their bodies to lower concentration of air.
(b) To acclimatize their bodies to lower temperature.
(c) To acclimatize their bodies to pressure.
(d) All of the above.

Answer: (d) All of the above.

6. The composition of the atmosphere makes it a dynamic entity, however there are four thermal layers. Which of the following is in the correct order from the surface of the earth?

(a) Thermosphere – Mesosphere – Stratosphere – Troposphere
(b) Troposphere – Mesosphere – Stratosphere – Thermosphere
(c) Troposphere – Stratosphere – Mesosphere – Thermosphere
(d) Thermosphere – Stratosphere – Mesosphere – Troposphere

Answer: (c) Troposphere – Stratosphere – Mesosphere – Thermosphere

7. Which amongst the following is not a domain of the Biosphere?

(a) Lithosphere
(b) Exosphere
(c) Hydrosphere
(d) Atmosphere

Answer: (b) Exosphere

8. _______ extends up to a height of about 400 km and is responsible for enabling radio communication.

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

Answer: (b) Ionosphere

9. The upper limit of the stratosphere is known as:

(a) Stratopause
(b) Statapause
(c) Upper strato
(d) Upper limital strato

Answer: (a) Stratopause

10. Name the uppermost layer in the structure of the atmosphere that gradually merges with interplanetary space.

(a) Ionosphere
(b) Exosphere
(c) Troposphere
(d) Mesosphere

Answer: (b) Exosphere

11. Water vapour is added to the atmosphere by _______

(a) evaporation
(b) transpiration
(c) respiration
(d) All of the above.

Answer: (d) All of the above.

12. Clouds and weather phenomenon occur in the Troposphere but some clouds are found in the Mesosphere. Why?

(a) Meteoric dust particles reflect sunlight causing wispy clouds.
(b) Some water particles reach the Mesosphere to form clouds.
(c) Ions from the ionosphere deflect sunlight giving the impression of clouds.
(d) None of the above.

Answer: (a) Meteoric dust particles reflect sunlight causing wispy clouds.

13. Which of the following are the functions of the atmosphere?

(a) Facilitates the cyclic exchange of gases
(b) Maintain of optimum temperature
(c) Protects the earth from harmful solar radiation
(d) All of the above.

Answer: (d) All of the above.

14. The decrease in the temperature is known as the:

(a) Normal temperature rate
(b) Decreased temperature rate
(c) Normal lapse rate
(d) Decreased lapse rate

Answer: (c) Normal lapse rate

15. Name the layer which contains ions electrically charged particles which create a sheet like display of light known as Aurora Borealis in the northern hemisphere.

(a) Ionosphere
(b) Exosphere
(c) Stratosphere
(d) Mesosphere

Answer: (a) Ionosphere

16. Which amongst the following is not a direct impact of Global Warming?

(a) Precipitation Change
(b) Radiation Balance
(c) Rise in Sea Level
(d) Diseases

Answer: (b) Radiation Balance

Short Answer Questions

1. What is known as atmosphere? State its composition.

Answer: The blanket of air surrounding the earth is known as the atmosphere.
The atmosphere is a mixture of many gases and tiny solid particles. A clean dry sample of air is made up of 78% of nitrogen and 21% of oxygen. The remaining 1% of air is made up of a number of gases, including carbon dioxide, water vapour, helium, hydrogen, argon, etc. Some particles like pollen from plants, dust from dust storms, ash from meteorites and volcanic eruptions, smoke from fire and salt particles from seas are also present in the lower layer of the atmosphere.

2. Name the four layers of the atmosphere. Give one function of the outer most layer.

Answer: On the basis of the characteristics of temperature and air pressure, there exist four thermal layers of the atmosphere. They are Troposphere, Stratosphere, Mesosphere and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere, with the Exosphere being the uppermost layer.

A characteristic of the Exosphere, the outermost layer, is that it merges gradually with interplanetary space.

3. What is known as troposphere? List any two characteristics of the troposphere.

Answer: The troposphere is the lowermost and densest layer of the atmosphere. Two characteristics of the troposphere are:

(i) Seventy-five per cent of the atmosphere is found in the troposphere and its concentration decreases as we go higher from ground level.
(ii) The troposphere is also characterised by regular decrease in temperature with altitude. This decrease in temperature is known as normal lapse rate. The average decrease is 1°C for every 166 metre altitude gained.

4. Mention the chief characteristics of stratosphere.

Answer: The chief characteristics of the stratosphere include:

The air is thin, cold and dry, with the temperature being about -55°C.
The Ozone layer lies within the stratosphere, generally found between the altitudes of 20 and 50 km.
Ozone absorbs the ultraviolet solar radiation coming from above. The insolation received from the sun is equal to that lost by it, which is why the temperature of the layer is constant; however, in the higher levels, temperature increases with height.
The lower layer of stratosphere has a virtual absence of water vapour and has constant temperature conditions, therefore, it is ideal for flying jet aircraft.
Temperature rises from -60°C at the base of the stratosphere to 0°C at the stratopause.

5. In which layer of atmosphere do all the weather conditions occur? Name the constituent gases of atmosphere which scientists consider responsible for climate change.

Answer: All weather phenomena take place in the troposphere.

The constituent gases of the atmosphere which are considered responsible for climate change, by disturbing the energy balance and increasing heat on Earth, are gases like carbon dioxide, methane, chlorofluorocarbons (CFCs), ozone, and water vapour, known as greenhouse gases.

6. Pratap was travelling by air from Kolkata to Chennai. There was heavy storm and rain in Bhubaneswar. Pratap’s flight had flown over Bhubaneswar during that storm and he did not feel any turbulence due to it. As a student of geography how would you explain this?

Answer: This can be explained by the fact that jet aircraft typically fly in the lower layer of the stratosphere. This layer has a virtual absence of water vapour and has constant temperature conditions. All weather phenomena, including storms, rain, and associated turbulences, occur in the troposphere, which is below the stratosphere. Therefore, by flying in the stratosphere, Pratap’s flight would have avoided the turbulence caused by the storm in Bhubaneswar.

7. What is known as Ozone Layer? What is leading to depletion of Ozone Layer in the atmosphere?

Answer: The Ozone Layer is a layer in the stratosphere of the atmosphere which keeps temperature constant in the lower levels and absorbs ultraviolet rays of the sun.

Depletion of the Ozone Layer in the atmosphere is led by several factors. Many chemicals, namely chlorine and bromine, are thought to cause the depletion. Chlorofluorocarbons (CFCs), used in refrigerators, aircraft, and air conditioners, escape into the atmosphere and break down in the stratosphere, producing chlorine atoms which destroy the Ozone layer. Volcanoes also play a role, as large eruptions give out sulphur dioxide, which speeds up destructive chemical reactions. Another cause is solar storms, which consist of coronal mass ejections and solar flares.

8. What would be the effect of Ozone Layer depletion? List the natural causes of Ozone Layer depletion.

Answer: The Ozone layer in the Stratosphere protects the earth from the ultraviolet rays of the sun. Its depletion would mean less protection from these harmful rays and contributes to Global Warming. The Ozone layer also protects the earth and its biosphere from extra heat. The natural causes of Ozone Layer depletion include:

(i) Volcanoes: Large eruptions give out sulphur dioxide, which speeds up destructive chemical reactions that deplete ozone.
(ii) Solar storms: These consist of coronal mass ejections and solar flares associated with explosions on the surface of the sun, which can also lead to the destruction of the Ozone layer.

9. Could Ozone in the lower layer of the atmosphere make up for loss of Ozone in the Ozone Layer? Give reasons to support your answer.

Answer: Ozone in the lower layer of the atmosphere, the troposphere, likely could not make up for the loss of Ozone in the Ozone Layer (stratosphere).

This is because in the troposphere, Ozone is generated only in small amounts. In contrast, in the stratosphere, at 20-50 km above sea level, it is present in significant amounts. The concentration of Ozone in the upper atmosphere (stratosphere) is protective as it absorbs the heat of the ultraviolet rays of the sun. The small and often localized amounts of tropospheric ozone would be insufficient to replicate this significant protective role performed by the stratospheric Ozone Layer.

10. What is known as Global Warming? Name important Greenhouse gases.

Answer: Global Warming is the rise in average mean temperature of the earth on account of enhanced concentration of greenhouse gases in the atmosphere.

Important Greenhouse gases include carbon dioxide, methane, chlorofluorocarbons (CFCs), ozone, and water vapour.

Structured Questions

1. (a) Define atmosphere. Name the four layers of atmosphere.

Answer: The blanket of air surrounding the earth is known as the atmosphere.
On the basis of the characteristics of temperature and air pressure there exist four thermal layers of the atmosphere. They are—Troposphere, Stratosphere, Mesosphere and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere.

(b) Mention any two functions of the atmosphere.

Answer: Two functions of the atmosphere are:

Air has weight and exerts pressure. Being pressed down it always remains in contact with land and water.
Carbon dioxide in air helps in absorption of heat and keeps the earth warm at night.

(c) Give a reason for each of the following:

(i) We find it difficult to breathe when we climb mountains.

Answer: We find it difficult to breathe when we climb mountains because layers of air become thinner at high altitudes. This is because less air is pressing down from above.

(ii) The atmosphere is the most dynamic entity.

Answer: The atmosphere is the most dynamic entity because of its composition. Large masses of air are being moved up and down and across the surface of the earth.

(iii) All the weather phenomena takes place in the troposphere.

Answer: All weather phenomena take place in the troposphere because the troposphere is responsible for many turbulences, and as a result of these turbulences all weather phenomena take place in this layer.

(d) Draw a well labelled diagram of the structure of the earth’s atmosphere.

Answer: See Fig. 12.2 of the Morning Star/Total Geography book or click here.

2. (a) Describe the structure of the atmosphere.

Answer: In the atmosphere, there are concentric layers of air. Each layer has different density. The upper layers press down the lower ones. So, the air of the lower layer is always heavier or denser, while the upper layers are thinner or less dense. In this way about 90 per cent of the mass of air lies within a height of about 20 km from the surface of the earth.

On the basis of the characteristics of temperature and air pressure there exist four thermal layers of the atmosphere. They are—Troposphere, Stratosphere, Mesosphere and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere.

Troposphere

Extent: The troposphere is the lowermost and densest layer. Its height varies from 18 km at the Equator to 8 km at the Poles.
Characteristics: Seventy-five per cent of the atmosphere is found in the troposphere and its concentration decreases as we go higher from ground level. The troposphere is also characterised by regular decrease in temperature with altitude. This decrease in temperature is known as normal lapse rate. The average decrease is 1°C for every 166 metre altitude gained. The troposphere is responsible for many turbulences. As a result of these turbulences all weather phenomena take place in this layer. The troposphere is heated more from below than from above. The upper limit of the troposphere is known as tropopause.

Stratosphere

Extent: This layer lies above the tropopause. It extends to a height of 50 km from sea level.
Characteristics: The air is thin, cold and dry. The temperature is about -55°C. The Ozone layer lies within the stratosphere. Ozone is generally found between the altitudes of 20 and 50 km. Ozone absorbs the ultraviolet solar radiation coming from above. The insolation received from the sun is equal to that lost by it. That is why the temperature of the layer is constant. In the higher levels, however, temperature increases with height. The lower layer of stratosphere has a virtual absence of water vapour and has constant temperature conditions, therefore, it is ideal for flying jet aircraft. Temperature rises from -60°C at the base of the stratosphere to 0°C at stratopause. The upper limit of the stratosphere is known as stratopause.

Mesosphere

Extent: This layer lies above the stratosphere and extends to a height of 80 km from ground level.
Characteristics: The temperature in this layer decreases with height and reaches a minimum of -110°C at the altitude of about 80 km near the mesopause, the upper limit of this layer. Due to reflected sunlight from meteoric dust particles there are wispy clouds found in this layer.

Ionosphere

Extent: It extends up to a height of about 400 km.
Characteristics: Ionosphere contains electrically charged particles called ions which create a sheet like display of light known as Aurora Borealis in the Northern Hemisphere and Aurora Australis in the Southern Hemisphere. Ions reflect radio waves back to the earth’s surface. This enables us to have wireless communication.

Exosphere

Extent: It is the uppermost layer in the structure of the atmosphere. It lies between 400 to 1500 km above the earth.
Characteristics: It merges gradually with interplanetary space. In this layer temperature increases with height. We know very little about the atmosphere extending beyond 640 km height from the sea level. In the Exosphere density becomes extremely low. The main gases here are lighter ones like hydrogen and helium.

(b) Explain the factors responsible for depletion of Ozone in atmosphere.

Answer: The factors responsible for depletion of Ozone in the atmosphere include:
Many chemicals namely chlorine and bromine are banned which are thought to cause the depletion of the Ozone layer.

Chlorofluorocarbons (CFCs) are regarded as the reason for the Ozone Hole near Antarctica. CFC gases are used in refrigerators, aircraft and air conditioners. CFC compounds escape into the atmosphere and finally break down in the stratosphere. They produce chlorine atoms which destroy the Ozone layer.

Volcanoes play a role in Ozone depletion. Large eruptions give out sulphur dioxide, which speed up destructive chemical reactions. Tropospheric Ozone increases especially in the Northern Hemisphere but it is smaller and localised at the eruption site.

Another cause of destruction of Ozone layer, discovered recently, are solar storms. These solar storms consist of coronal mass ejections and solar flares associated with explosions on the surface of the sun.

The formation of the Ozone hole has been attributed largely to the activities of man. Ozone depletion resulting in Ozone hole is more common to Antarctica where temperatures are the lowest. Due to bitterly cold Antarctic winter, the stratospheric ice clouds promote production of chemically active chlorine and bromine. This, in turn, leads to Ozone destruction when sunlight returns in the Antarctic spring.

(c) State any three factors that lead to Global Warming.

Answer: Three factors that lead to Global Warming are:

Destruction of Ozone Layer: The Ozone layer in the Stratosphere protects the earth from the ultraviolet rays of the sun and its depletion contributes to Global Warming.
Greenhouse Effect in the Atmosphere: Excess accumulation of some gases like carbon dioxide, methane, chlorofluorocarbons (CFCs), ozone and water vapour are responsible for disturbing the energy balance and thus increasing heat on the earth. Fossil fuel based industries and human lifestyle have resulted in an unprecedented rise of these gases, known as greenhouse gases. Greenhouse gases in the atmosphere allow the near infrared rays from the sun to penetrate into the earth. But these gases do not allow the heat radiated by the heated earth to easily dissipate into space. Thus, by preventing heat rays to escape into the outer space the greenhouse gases add to the heat already available on the earth’s surface. The increase in temperature due to the concentration of the greenhouse gases is known as the greenhouse effect.
Deforestation: Clearing away of forests and forest ecosystems on a large scale have posed several dangers to life on earth. Trees are essential for absorbing excess carbon dioxide in air. In their absence, winds blow away the top soil as dust into the atmosphere. The dust in the atmosphere plays a key role in reflecting terrestrial radiation back to earth.

(d) Draw a well labelled diagram to explain the Greenhouse Effect.

Answer: See Fig. 12.4 of Morning Star/Total Geography or click here.

Thinking Skills

1. Do you think any one layer of the atmosphere is more significant than the other layers? If yes, which one and why? If not, reasons to support your answer.

Answer: Yes, I believe the troposphere is the most significant layer of the atmosphere. It contains about 75% of the atmospheric mass and is where all weather phenomena occur. This makes it directly relevant to life on Earth. The presence of oxygen and water vapour in this layer supports respiration and the water cycle, which are essential for survival.

2. How is the atmosphere responsible for Global Warming? What changes human beings can made in their lifestyle to preserve the atmosphere and check Global Warming?

Answer: The atmosphere is responsible for global warming mainly due to the greenhouse gases trapped in it. Gases like carbon dioxide, methane, chlorofluorocarbons, and water vapour form a layer that allows sunlight to enter but traps heat, preventing it from escaping back into space. This raises the Earth’s temperature. To help preserve the atmosphere and check global warming, people can reduce the use of fossil fuels, switch to renewable energy sources, avoid products with CFCs, reduce deforestation, and adopt sustainable practices like using public transport, conserving electricity, and planting trees.

3. Mention one significant effect of climate change that affects you.

Answer: One significant effect of climate change that affects me is the change in rainfall patterns. It leads to unpredictable monsoons, with some areas experiencing heavy floods and others facing drought. This affects agriculture, water supply, and day-to-day life, especially in regions that rely heavily on seasonal rains.

Project Work

Forest fires are becoming more frequent and disastrous sparking a global outrage. Prepare a project report on the causes and the effects, both short term and long term, offorest fires.

Answer: Do it yourself. Here are the instructions:

Use a physical map of the world or India showing major layers of the atmosphere. If using an outline map, make sure it is labelled correctly.
Identify and label the four main thermal layers of the atmosphere in correct order starting from the surface of the Earth:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere (with subdivisions: Ionosphere and Exosphere)
Use different coloured pencils to shade each atmospheric layer distinctly.
Draw and label the approximate height range for each layer:
- Troposphere: up to 18 km (equator), 8 km (poles)
- Stratosphere: 18–50 km
- Mesosphere: 50–80 km
- Thermosphere: 80–400+ km
- Exosphere: 400–1500 km
Mark the tropopause, stratopause, mesopause, and indicate where the ozone layer lies (within the stratosphere at 20–50 km).
Draw arrows to show the movement of heat, water vapour, and gases like oxygen, nitrogen, and carbon dioxide between layers.
Include notes or labels explaining:
- Weather phenomena occur in the troposphere.
- Ozone layer absorbs harmful UV rays in the stratosphere.
- The ionosphere reflects radio waves for communication.
- The exosphere merges into space and contains light gases like hydrogen and helium.
Title your map clearly: “Structure of the Atmosphere”.
Use a scale and north direction arrow if required.
Keep your map neat and do not overcrowd labels.

Extras

Additional MCQs

1. Which envelope of air surrounds the Earth?

A. Biosphere
B. Lithosphere
C. Atmosphere
D. Hydrosphere

Answer: C. Atmosphere

2. What percentage of clean dry air is nitrogen?

A. 21%
B. 1%
C. 78%
D. 75%

Answer: C. 78%

3. Which gas dilutes oxygen and slows down oxidation?

A. Carbon dioxide
B. Nitrogen
C. Argon
D. Helium

Answer: B. Nitrogen

4. Which constituent of air is essential for precipitation?

A. Carbon dioxide
B. Water vapour
C. Ozone
D. Nitrogen

Answer: B. Water vapour

5. Which particles act as nuclei for raindrop formation?

A. Pollen
B. Salt
C. Volcanic ash
D. All of the above

Answer: D. All of the above

6. Approximately what fraction of the total air mass lies below 5 km altitude?

A. One quarter
B. One half
C. Three quarters
D. All

Answer: B. One half

7. By which force is the atmosphere held close to Earth?

A. Magnetism
B. Gravity
C. Centrifugal force
D. Friction

Answer: B. Gravity

8. Which layer contains about 75% of the atmosphere’s mass?

A. Troposphere
B. Stratosphere
C. Mesosphere
D. Exosphere

Answer: A. Troposphere

9. What is the average normal lapse rate in the troposphere?

A. 1 °C per 100 m
B. 2 °C per 100 m
C. 1 °C per 166 m
D. 1 °F per 166 m

Answer: C. 1 °C per 166 m

10. What is the upper boundary of the troposphere called?

A. Tropopause
B. Stratopause
C. Mesopause
D. Thermopause

Answer: A. Tropopause

11. Above which altitude does the stratosphere extend?

A. 8 km
B. 18 km
C. 50 km
D. 80 km

Answer: C. 50 km

12. What is the approximate temperature at the base of the stratosphere?

A. 0 °C
B. -55 °C
C. 15 °C
D. -110 °C

Answer: B. -55 °C

13. Which layer of the atmosphere contains the ozone layer?

A. Troposphere
B. Stratosphere
C. Mesosphere
D. Exosphere

Answer: B. Stratosphere

14. What drives the formation of ozone in the stratosphere?

A. Volcanic eruptions
B. Solar radiation
C. Lightning
D. Combustion

Answer: B. Solar radiation

15. Why is the lower stratosphere ideal for flying jet aircraft?

A. High pressure
B. Constant temperature
C. Abundant moisture
D. Strong winds

Answer: B. Constant temperature

16. What is the upper limit of the stratosphere called?

A. Tropopause
B. Stratopause
C. Mesopause
D. Thermopause

Answer: B. Stratopause

17. To what altitude does the mesosphere extend?

A. 20 km
B. 50 km
C. 80 km
D. 400 km

Answer: C. 80 km

18. What is the temperature at the mesopause?

A. -55 °C
B. -110 °C
C. 0 °C
D. 15 °C

Answer: B. -110 °C

19. What causes wispy clouds in the mesosphere?

A. Reflected sunlight
B. Radio waves
C. Cosmic rays
D. Gas condensation

Answer: A. Reflected sunlight

20. Which layer contains electrically charged particles creating auroras?

A. Mesosphere
B. Ionosphere
C. Stratosphere
D. Exosphere

Answer: B. Ionosphere

21. Up to what altitude does the ionosphere extend?

A. 80 km
B. 150 km
C. 400 km
D. 1500 km

Answer: C. 400 km

22. Which phenomenon is enabled by the ionosphere reflecting radio waves?

A. Satellite TV
B. GPS errors
C. Wireless communication
D. UV protection

Answer: C. Wireless communication

23. Which layer is the outermost, merging gradually with space?

A. Mesosphere
B. Thermosphere
C. Exosphere
D. Ionosphere

Answer: C. Exosphere

24. Which gases dominate the exosphere?

A. Nitrogen and oxygen
B. Carbon dioxide and water vapour
C. Hydrogen and helium
D. Argon and neon

Answer: C. Hydrogen and helium

25. What percentage of air is oxygen?

A. 1%
B. 21%
C. 50%
D. 78%

Answer: B. 21%

26. In which layer does nearly all weather phenomena occur?

A. Stratosphere
B. Troposphere
C. Mesosphere
D. Exosphere

Answer: B. Troposphere

27. Which gas absorbs harmful ultraviolet solar radiation?

A. Nitrogen
B. Ozone
C. Carbon dioxide
D. Argon

Answer: B. Ozone

28. Approximately one molecule in how many in the atmosphere is ozone?

A. 1 in 200
B. 1 in 2 000
C. 1 in 2 000 000
D. 1 in 20 000 000

Answer: C. 1 in 2 000 000

29. Which compounds are chiefly responsible for Antarctic ozone depletion?

A. Methane
B. Chlorofluorocarbons
C. Sulphur dioxide
D. Carbon dioxide

Answer: B. Chlorofluorocarbons

30. Which natural event emits sulphur dioxide that accelerates ozone destruction?

A. Solar storms
B. Earthquakes
C. Volcanic eruptions
D. Tsunamis

Answer: C. Volcanic eruptions

31. Which phenomenon involving coronal mass ejections leads to ozone depletion?

A. Greenhouse effect
B. Solar storms
C. Jet exhaust
D. Acid rain

Answer: B. Solar storms

32. When was the largest ozone hole observed near Antarctica?

A. March 1995
B. September 2000
C. July 2010
D. December 1987

Answer: B. September 2000

33. Why is ozone hole formation more common over Antarctica than the Arctic?

A. Higher CFCs
B. Colder winter temperatures
C. Stronger winds
D. Greater sunlight

Answer: B. Colder winter temperatures

34. Which gas is the primary driver of global warming by trapping infrared radiation?

A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Argon

Answer: C. Carbon dioxide

35. What name is given to the trapping of heat by greenhouse gases?

A. Ozone effect
B. Coriolis effect
C. Greenhouse effect
D. Rain shadow

Answer: C. Greenhouse effect

36. Which organisation used the term “Global Warming” to raise awareness?

A. NASA
B. IPCC
C. UNEP
D. WHO

Answer: C. UNEP

37. Which process involves large-scale clearing of forests contributing to warming?

A. Afforestation
B. Deforestation
C. Urbanisation
D. Farming

Answer: B. Deforestation

38. Over the last century, sea levels have risen by roughly how much?

A. 1–5 cm
B. 10–25 cm
C. 50–60 cm
D. 1 m

Answer: B. 10–25 cm

39. By 2100, sea levels are predicted to rise between how many feet?

A. 0.5–1
B. 1–2
C. 2.5–6.5
D. 10–12

Answer: C. 2.5–6.5

40. Which region is expected to experience decreased winter rainfall?

A. Higher latitudes
B. Lower latitudes
C. Southern Asia
D. Eastern Asia

Answer: B. Lower latitudes

41. Under global warming, species are expected to migrate predominantly in which direction?

A. Equatorward
B. Poleward
C. Eastward
D. Westward

Answer: B. Poleward

42. Which resource is likely to worsen more due to population pressure than climate change?

A. Water
B. Mineral
C. Forest
D. Fisheries

Answer: A. Water

43. Which disease may reappear due to changes in temperature and precipitation?

A. Cholera
B. Malaria
C. Influenza
D. Tuberculosis

Answer: B. Malaria

44. How many domains constitute the Earth’s biosphere?

A. Two
B. Three
C. Four
D. One

Answer: B. Three

45. In which state does the hydrosphere exist?

A. Solid
B. Liquid
C. Gaseous
D. Plasma

Answer: B. Liquid

46. In which state does the lithosphere exist?

A. Solid
B. Liquid
C. Gaseous
D. Plasma

Answer: A. Solid

47. Approximately what percentage of the atmosphere’s mass lies within 20 km of the surface?

A. 50%
B. 75%
C. 90%
D. 100%

Answer: C. 90%

48. How high is the troposphere at the Equator?

A. 8 km
B. 5 km
C. 18 km
D. 20 km

Answer: C. 18 km

49. How high is the troposphere at the poles?

A. 5 km
B. 8 km
C. 18 km
D. 20 km

Answer: B. 8 km

50. Which boundary separates the mesosphere from the thermosphere?

A. Tropopause
B. Stratopause
C. Mesopause
D. Thermopause

Answer: C. Mesopause

51. Which boundary separates the stratosphere from the mesosphere?

A. Tropopause
B. Stratopause
C. Mesopause
D. Thermopause

Answer: B. Stratopause

52. Which abbreviation refers to chemicals that deplete the ozone layer?

A. CO2
B. CH4
C. CFCs
D. SO2

Answer: C. CFCs

53. The rise in average mean temperature of the Earth caused by enhanced greenhouse gas concentration is known as

A. Greenhouse effect
B. Global warming
C. Ozone depletion
D. Climate variability

Answer: B. Global warming

54. Which process occurs due to physical contact between the atmosphere and Earth’s land and water?

A. Erosion
B. Gas exchange
C. Radiation
D. Convection

Answer: B. Gas exchange

Additional Assertion and Reason

1. Assertion (A): Air is thinner at high altitudes.
Reason (R): Less air is pressing down from above at higher altitudes.