Introduction
The Atmosphere is an important chapter of Class 10 Chemistry that explains the composition, structure, and significance of Earth’s gaseous envelope. Students learn about the major gases present in the atmosphere, the different atmospheric layers, the ozone layer, greenhouse gases, and the vital role the atmosphere plays in supporting life on Earth. The chapter also introduces important environmental issues such as air pollution, acid rain, ozone depletion, global warming, and methods for protecting the atmosphere.
Students study the sources and effects of common air pollutants, including carbon monoxide, sulfur dioxide, nitrogen oxides, particulate matter, and chlorofluorocarbons (CFCs). They also learn how these pollutants affect human health, ecosystems, climate, and historical monuments. Understanding atmospheric chemistry helps students appreciate the importance of environmental conservation and sustainable development. These concepts are frequently tested in school and board examinations and are highly relevant to modern environmental challenges.
On this page, you will find carefully selected Class 10 Chemistry Chapter 5 MCQs with answers and explanations, along with learning outcomes, quick revision notes, important definitions, important chemical equations, exam tips, and common mistakes to help you prepare effectively for your examinations.
Learning Outcomes
After studying this chapter, students will be able to:
- Describe the composition of Earth’s atmosphere.
- Identify the different layers of the atmosphere and their characteristics.
- Explain the importance of the ozone layer.
- Describe the greenhouse effect and global warming.
- Explain the causes and effects of air pollution.
- Understand the formation of acid rain and photochemical smog.
- Identify methods for controlling atmospheric pollution.
Quick Notes – Chapter Summary
- Nitrogen (N₂) makes up about 78% of Earth’s atmosphere.
- Oxygen (O₂) accounts for about 21% of atmospheric air.
- The atmosphere consists of the troposphere, stratosphere, mesosphere, and thermosphere.
- The ozone layer is located in the stratosphere and absorbs harmful ultraviolet (UV) radiation.
- Carbon monoxide is a poisonous gas produced by incomplete combustion.
- Sulfur dioxide and nitrogen oxides contribute to acid rain.
- Greenhouse gases trap heat and cause global warming.
- Ground-level ozone is a harmful secondary pollutant.
- Photochemical smog forms through reactions involving NOₓ, volatile organic compounds (VOCs), and sunlight.
- CFCs are responsible for ozone layer depletion.
- PM₂.₅ and PM₁₀ are important indicators of particulate air pollution.
- Reducing fossil fuel consumption and increasing tree plantation help protect the atmosphere.
Important Definitions
Atmosphere: The layer of gases surrounding the Earth.
Air Pollution: The contamination of the atmosphere by harmful substances.
Ozone Layer: A region in the stratosphere containing a high concentration of ozone that absorbs harmful ultraviolet radiation.
Greenhouse Effect: The warming of Earth’s surface caused by greenhouse gases trapping infrared radiation.
Global Warming: The gradual increase in Earth’s average temperature due to increased greenhouse gas concentrations.
Acid Rain: Rainfall with a low pH caused mainly by sulfur dioxide (SO₂) and nitrogen oxides (NOₓ).
Photochemical Smog: A type of air pollution formed when sunlight reacts with nitrogen oxides and volatile organic compounds.
Particulate Matter (PM): Tiny solid or liquid particles suspended in air that can affect human health.
Important Chemical Equations
Formation of Ozone
O₂ + UV → 2O
O + O₂ → O₃
Formation of Sulfuric Acid (Acid Rain)
2SO₂ + O₂ → 2SO₃
SO₃ + H₂O → H₂SO₄
Formation of Nitric Acid (Simplified)
4NO₂ + O₂ + 2H₂O → 4HNO₃
Complete Combustion of Carbon
C + O₂ → CO₂
Incomplete Combustion of Carbon
2C + O₂ → 2CO
Important Concepts
Pollution control measures.
Composition of the atmosphere.
Atmospheric layers.
Ozone layer and UV protection.
Air pollutants and their sources.
Greenhouse effect.
Global warming.
Acid rain.
Photochemical smog.
Ozone depletion.
Air quality and particulate matter.
Class 10 Chemistry Chapter 5 – The Atmosphere (Environmental Chemistry I) MCQs
1. Which gas makes up the largest proportion of dry air?
- A. Oxygen
- B. Nitrogen (N2) ✅
- C. Carbon dioxide
- D. Argon
Explanation: Approximately 78% of Earth’s dry atmosphere is nitrogen by volume.
2. Which atmospheric layer contains the ozone layer?
- A. Troposphere
- B. Stratosphere ✅
- C. Mesosphere
- D. Thermosphere
Explanation: Ozone (O3) is concentrated mainly in the stratosphere, providing protection from harmful UV radiation.
3. Ozone in the stratosphere is formed by which simplified reaction (photochemical)?
- A. O2 + O → O3
- B. O2 + hv (UV) → 2O; O + O2 → O3 ✅
- C. 2O3 → 3O2
- D. O + O → O2
Explanation: UV light splits O2 into O atoms; these combine with O2 to make O3.
4. Which pollutant is primarily responsible for respiratory problems and is a major product of incomplete combustion?
- A. Sulfur dioxide (SO2)
- B. Carbon monoxide (CO) ✅
- C. Ozone (O3)
- D. Nitrogen gas (N2)
Explanation: CO is produced by incomplete combustion and binds to hemoglobin, reducing oxygen transport.
5. Acid rain is mainly caused by the atmospheric conversion of which gases?
- A. CO2 and N2
- B. SO2 and NOx (NO, NO2) ✅
- C. O2 and H2
- D. NH3 and CH4
Explanation: SO2 and nitrogen oxides react with water to form sulfuric and nitric acids, causing acid rain.
6. Which of the following reactions shows formation of sulfuric acid from sulfur dioxide?
- A. SO2 + H2O → H2SO4
- B. 2SO2 + O2 → 2SO3; SO3 + H2O → H2SO4 ✅
- C. SO2 + O → SO3
- D. SO2 → S + O2
Explanation: SO2 oxidizes to SO3, which forms H2SO4 with water.
7. What is ‘smog’ commonly associated with?
- A. High ozone concentration in stratosphere
- B. Photochemical pollution in urban areas (NOx + VOCs + sunlight) ✅
- C. Only volcanic ash
- D. Dissolved gases in rainwater
Explanation: Photochemical smog forms from NOx and volatile organic compounds under strong sunlight, producing ground-level ozone and particulates.
8. Ground-level ozone (O3) is harmful because:
- A. It protects against UV
- B. It irritates lungs and damages vegetation ✅
- C. It is inert and harmless
- D. It removes CO from air
Explanation: Unlike stratospheric ozone, ground-level ozone is a pollutant that harms respiratory health and plants.
9. The greenhouse effect is primarily caused by which gases?
- A. Oxygen and nitrogen
- B. Carbon dioxide (CO2), methane (CH4), water vapour, and others ✅
- C. Argon and neon
- D. Helium and hydrogen
Explanation: Greenhouse gases trap infrared radiation and warm Earth’s surface; CO2 and CH4 are major contributors.
10. Which human activity is the largest source of increased atmospheric CO2?
- A. Natural respiration of plants
- B. Burning of fossil fuels (coal, oil, gas) ✅
- C. Photosynthesis
- D. Ocean evaporation
Explanation: Fossil fuel combustion is the major anthropogenic source of CO2 emissions.
11. Which pollutant is a major product of the combustion of sulfur-containing fuels?
- A. NO
- B. SO2 ✅
- C. CO2
- D. O3
Explanation: Burning sulfur-containing coal or oil produces sulfur dioxide (SO2), a gas that contributes to acid rain.
12. Which simple practice can help reduce atmospheric pollution locally?
- A. Increase burning of biomass
- B. Use more two-stroke engines
- C. Promote public transport and reduce vehicle use ✅
- D. Remove all trees in cities
Explanation: Reducing vehicle use lowers emissions of NOx, CO, VOCs and particulates.
13. Which of the following is NOT a primary air pollutant?
- A. Particulate matter (PM)
- B. Carbon monoxide (CO)
- C. Ozone (O3) ✅
- D. Sulfur dioxide (SO2)
Explanation: Primary pollutants are emitted directly; ozone at ground level is typically a secondary pollutant formed from reactions in air.
14. What is the major environmental effect of acid rain on freshwater ecosystems?
- A. Increase in pH making water alkaline
- B. Decrease in pH harming aquatic life (fish kills) ✅
- C. Increase in dissolved oxygen
- D. Immediate desalination
Explanation: Acid rain lowers the pH of lakes and rivers, which can be lethal to many aquatic organisms.
15. The depletion of stratospheric ozone is mainly linked to which group of chemicals?
- A. CO2
- B. NOx
- C. Chlorofluorocarbons (CFCs) ✅
- D. Sulfur compounds
Explanation: CFCs release Cl atoms in the stratosphere that catalytically destroy ozone molecules.
16. Which international agreement aims to reduce substances that deplete the ozone layer?
- A. Kyoto Protocol
- B. Paris Agreement
- C. Montreal Protocol ✅
- D. Basel Convention
Explanation: The Montreal Protocol (1987) phased out many ozone-depleting substances like CFCs.
17. Photochemical smog formation is favoured by which weather conditions?
- A. Cool, rainy and windy
- B. Sunny, hot, and stagnant air (little wind) ✅
- C. Cold and snowy
- D. High humidity only
Explanation: Strong sunlight drives photochemical reactions; stagnant conditions allow pollutants to accumulate.
18. Which measurement is commonly used to indicate small-particle air pollution harmful to health?
- A. pH of rain
- B. CO2 concentration
- C. PM2.5 or PM10 concentration ✅
- D. O3 in stratosphere
Explanation: PM2.5/PM10 are particulate matter size categories commonly used to assess air quality and health risks.
Exam Tips
- Memorize the percentage composition of atmospheric gases.
- Learn the characteristics of each atmospheric layer.
- Understand the causes and effects of acid rain, greenhouse effect, and ozone depletion.
- Practice important chemical equations related to atmospheric chemistry.
- Revise major pollutants, their sources, and their environmental impacts.
Common Mistakes
❌ Confusing the greenhouse effect with ozone depletion.
❌ Thinking all ozone is harmful.
❌ Forgetting that ground-level ozone is a pollutant while stratospheric ozone is beneficial.
❌ Confusing carbon monoxide with carbon dioxide.
❌ Assuming acid rain is caused only by carbon dioxide.
Conclusion
The atmosphere is essential for supporting life on Earth by providing oxygen, regulating temperature, and protecting living organisms from harmful ultraviolet radiation. Understanding atmospheric composition, pollution, greenhouse gases, acid rain, and ozone depletion enables students to appreciate the importance of environmental conservation and sustainable practices. Regular revision of the important concepts, chemical equations, and MCQs will strengthen conceptual understanding and improve performance in school and board examinations.