🌍 Natural Resources – Class 9 Science MCQs

Section 3: Soil, Biogeochemical Cycles & Fossil Fuels (Q51–Q75)

Q51. The uppermost layer of Earth that supports plant growth is:

A. Sand
B. Soil
C. Rocks
D. Humus

✅ Correct Answer: B. Soil

Explanation:

• Soil is a mixture of minerals, organic matter, water, and air → essential for plants.

Q52. Which of these is NOT a factor of soil formation?

A. Climate
B. Parent rock
C. Time
D. Electricity

✅ Correct Answer: D. Electricity

Q53. Soil erosion means:

A. Formation of soil
B. Removal of top fertile layer of soil
C. Adding humus to soil
D. Increasing soil fertility

✅ Correct Answer: B. Removal of top fertile layer of soil

Q54. Which activity increases soil erosion?

A. Afforestation
B. Deforestation
C. Mulching
D. Terrace farming

✅ Correct Answer: B. Deforestation

Q55. Which method is used to prevent soil erosion on slopes?

A. Crop rotation
B. Terrace farming
C. Overgrazing
D. Over-irrigation

✅ Correct Answer: B. Terrace farming

Q56. The nitrogen cycle involves conversion of:

A. Nitrogen → Oxygen
B. Atmospheric nitrogen → usable nitrogen compounds
C. CO₂ → O₂
D. Carbon → Nitrogen

✅ Correct Answer: B. Atmospheric nitrogen → usable nitrogen compounds

Q57. Nitrogen fixation is done by:

A. Rhizobium bacteria
B. Fungi
C. Virus
D. Algae only

✅ Correct Answer: A. Rhizobium bacteria

Q58. The release of nitrogen back into atmosphere is called:

A. Nitrification
B. Denitrification
C. Assimilation
D. Ammonification

✅ Correct Answer: B. Denitrification

Q59. In the nitrogen cycle, nitrifying bacteria convert:

A. NH₃ → NO₂⁻ / NO₃⁻
B. NO₂⁻ → N₂
C. CO₂ → O₂
D. NH₃ → CH₄

✅ Correct Answer: A. NH₃ → NO₂⁻ / NO₃⁻

Q60. Carbon cycle is maintained by:

A. Photosynthesis and respiration
B. Nitrogen fixation
C. Combustion only
D. Soil erosion

✅ Correct Answer: A. Photosynthesis and respiration

Q61. Which process adds CO₂ into atmosphere?

A. Photosynthesis
B. Respiration
C. Combustion
D. Both B and C

✅ Correct Answer: D. Both B and C

Q62. Which process removes CO₂ from atmosphere?

A. Respiration
B. Photosynthesis
C. Combustion
D. Volcanoes

✅ Correct Answer: B. Photosynthesis

Q63. Oxygen cycle is linked to:

A. Photosynthesis and respiration
B. Water cycle
C. Soil erosion
D. Nitrogen cycle

✅ Correct Answer: A. Photosynthesis and respiration

Q64. Fossil fuels are formed from:

A. Rocks
B. Dead plants and animals
C. Soil
D. Minerals

✅ Correct Answer: B. Dead plants and animals

Q65. Which of these is NOT a fossil fuel?

A. Coal
B. Petroleum
C. Natural gas
D. Wood

✅ Correct Answer: D. Wood

Q66. Petroleum is formed from:

A. Dead marine plants and animals
B. Dead forests only
C. Volcanoes
D. Soil erosion

✅ Correct Answer: A. Dead marine plants and animals

Q67. The main component of natural gas is:

A. CO₂
B. Methane (CH₄)
C. Ethanol
D. Propane

✅ Correct Answer: B. Methane (CH₄)

Q68. Coal is formed from:

A. Marine animals
B. Forest vegetation under pressure
C. Minerals
D. Soil

✅ Correct Answer: B. Forest vegetation under pressure

Q69. Which of these is NOT a consequence of burning fossil fuels?

A. Air pollution
B. Global warming
C. Ozone depletion
D. Increase in soil fertility

✅ Correct Answer: D. Increase in soil fertility

Q70. Excess use of fossil fuels leads to:

A. Acid rain
B. Global warming
C. Respiratory diseases
D. All of these

✅ Correct Answer: D. All of these

Q71. Fossil fuels are:

A. Renewable
B. Non-renewable
C. Inexhaustible
D. Man-made

✅ Correct Answer: B. Non-renewable

Q72. Which of these is a renewable source of energy?

A. Petroleum
B. Coal
C. Solar energy
D. Natural gas

✅ Correct Answer: C. Solar energy

Q73. Excessive use of nitrogen fertilizers leads to:

A. Increase in O₂
B. Eutrophication
C. More rainfall
D. Ozone depletion

✅ Correct Answer: B. Eutrophication

Q74. Which cycle maintains balance of carbon on Earth?

A. Oxygen cycle
B. Nitrogen cycle
C. Carbon cycle
D. Water cycle

✅ Correct Answer: C. Carbon cycle

Q75. Which human activity increases CO₂ in atmosphere?

A. Photosynthesis
B. Combustion of fossil fuels
C. Afforestation
D. Rainwater harvesting

✅ Correct Answer: B. Combustion of fossil fuels

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