🌍 Natural Resources – Class 9 Science MCQs

Section 1: Air, Atmosphere & Oxygen Cycle (Q1–Q25)

Q1. The atmosphere mainly contains nitrogen and oxygen in the ratio of:

A. 50:50
B. 78:21
C. 21:78
D. 70:30

✅ Correct Answer: B. 78:21

Explanation:

• A, C, D: Incorrect as nitrogen is the major gas, ~78%.
• B: Correct, nitrogen 78%, oxygen 21%.

Q2. The layer of atmosphere containing ozone is:

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

✅ Correct Answer: B. Stratosphere

Explanation:

• A: Troposphere has weather phenomena.
• B: Correct, ozone layer is in stratosphere.
• C & D: Higher layers, no ozone concentration.

Q3. Ozone layer protects life on Earth from:

A. Infrared rays
B. Ultraviolet rays
C. X-rays
D. Visible light

✅ Correct Answer: B. Ultraviolet rays

Q4. Greenhouse effect is caused mainly by:

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

✅ Correct Answer: B. Carbon dioxide

Explanation:

• CO₂, methane, water vapour trap heat, causing global warming.

Q5. The gas essential for photosynthesis is:

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

✅ Correct Answer: B. Carbon dioxide

Q6. Which process releases oxygen into the atmosphere?

A. Respiration
B. Combustion
C. Photosynthesis
D. Nitrogen fixation

✅ Correct Answer: C. Photosynthesis

Q7. Which process consumes oxygen?

A. Photosynthesis
B. Combustion
C. Evaporation
D. None

✅ Correct Answer: B. Combustion

Q8. Oxygen cycle is maintained by:

A. Respiration and photosynthesis
B. Nitrogen fixation
C. Ozone formation
D. Evaporation

✅ Correct Answer: A. Respiration and photosynthesis

Q9. Which gas in atmosphere is inert and does not react?

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

✅ Correct Answer: B. Argon

Q10. Smog is caused due to:

A. Smoke + Fog
B. CO₂ + O₂
C. N₂ + CO₂
D. Ozone depletion

✅ Correct Answer: A. Smoke + Fog

Q11. The phenomenon responsible for rain is:

A. Combustion
B. Evaporation & condensation
C. Respiration
D. Photosynthesis

✅ Correct Answer: B. Evaporation & condensation

Q12. Which is not a greenhouse gas?

A. CO₂
B. O₂
C. CH₄
D. H₂O vapour

✅ Correct Answer: B. O₂

Q13. What is “acid rain”?

A. Rainwater mixed with CO₂ only
B. Rainwater with H₂SO₄ and HNO₃
C. Pure rainwater
D. Alkaline water droplets

✅ Correct Answer: B. Rainwater with H₂SO₄ and HNO₃

Explanation:

• Acid rain forms when SO₂ and NO₂ mix with rain.

Q14. Acid rain damages:

A. Monuments
B. Crops
C. Aquatic life
D. All of these

✅ Correct Answer: D. All of these

Q15. Main source of SO₂ in atmosphere is:

A. Plants
B. Vehicles and industries
C. Oceans
D. Volcanoes

✅ Correct Answer: B. Vehicles and industries

Q16. “Hole in ozone layer” is caused by:

A. CO₂
B. SO₂
C. CFCs (Chlorofluorocarbons)
D. O₂

✅ Correct Answer: C. CFCs (Chlorofluorocarbons)

Q17. Global warming leads to:

A. Rise in sea level
B. Melting of glaciers
C. Climate change
D. All of these

✅ Correct Answer: D. All of these

Q18. The layer where weather phenomena occur is:

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

✅ Correct Answer: B. Troposphere

Q19. Which of these is not an air pollutant?

A. SO₂
B. NO₂
C. O₂
D. CO

✅ Correct Answer: C. O₂

Q20. The main source of CO in cities is:

A. Volcanoes
B. Industries
C. Incomplete combustion of fuels in vehicles
D. Plants

✅ Correct Answer: C. Incomplete combustion of fuels in vehicles

Q21. The gas needed for burning fuels is:

A. O₂
B. CO₂
C. N₂
D. CH₄

✅ Correct Answer: A. O₂

Q22. Photosynthesis balances atmosphere by:

A. Removing O₂
B. Adding CO₂
C. Removing CO₂, releasing O₂
D. Adding water

✅ Correct Answer: C. Removing CO₂, releasing O₂

Q23. Which human activity increases CO₂ in atmosphere?

A. Deforestation
B. Burning of fossil fuels
C. Industrialisation
D. All of these

✅ Correct Answer: D. All of these

Q24. The process that reduces atmospheric CO₂ is:

A. Respiration
B. Photosynthesis
C. Burning
D. Decomposition

✅ Correct Answer: B. Photosynthesis

Q25. Greenhouse effect leads to:

A. Cooling of Earth
B. Heating of Earth
C. More rainfall only
D. Ozone depletion

✅ Correct Answer: B. Heating of Earth

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