Try each question on your own first. Use the Show Answer button only after you have selected your option, then read the explanation and revise the related concept from your chapter notes.
1. The life-supporting zone of the Earth where the atmosphere, hydrosphere, and lithosphere interact is called:
A. Stratosphere
B. Biosphere
C. Ionosphere
D. Troposphere
Answer: B. Biosphere
Explanation: The biosphere is the global ecological system integrating all living beings and their relationships with the lithosphere, hydrosphere, and atmosphere.
2. Which gas constitutes approximately 78% of Earth's atmosphere?
A. Oxygen
B. Carbon Dioxide
C. Nitrogen
D. Argon
Answer: C. Nitrogen
Explanation: Earth's atmosphere is composed of about 78% nitrogen, 21% oxygen, and small amounts of carbon dioxide, argon, and water vapor.
3. What causes wind movement across Earth's surface?
A. Uneven heating of land and water bodies by solar radiation
B. Rotation of Earth only
C. Gravitational pull of the Moon
D. High humidity levels
Answer: A. Uneven heating of land and water bodies by solar radiation
Explanation: Solar heating causes air over land to warm faster than over water, creating convection currents that generate winds.
4. Which organism plays a crucial role as a biological weathering agent in soil formation?
A. Earthworms
B. Lichens
C. Algae
D. Fungi
Answer: B. Lichens
Explanation: Lichens growing on rock surfaces release substances that cause the rock to powder down, aiding soil formation.
5. Which atmospheric layer contains the protective ozone layer that absorbs harmful UV radiation?
A. Troposphere
B. Stratosphere
C. Mesosphere
D. Exosphere
Answer: B. Stratosphere
Explanation: The ozone layer is located in the stratosphere and blocks harmful ultraviolet (UV) radiation from reaching Earth's surface.
6. Which man-made chemicals are primarily responsible for ozone layer depletion?
A. Methane
B. Chlorofluorocarbons (CFCs)
C. Carbon Monoxide
D. Sulfur Dioxide
Answer: B. Chlorofluorocarbons (CFCs)
Explanation: CFCs contain chlorine atoms that react with ozone molecules in the upper atmosphere, breaking them down into oxygen.
7. Nitrogen fixation in soil is primarily carried out by which symbiotic bacterium found in root nodules of leguminous plants?
A. Azotobacter
B. Rhizobium
C. Nitrosomonas
D. Nitrobacter
Answer: B. Rhizobium
Explanation: *Rhizobium* bacteria reside in the root nodules of pulses/legumes and convert atmospheric nitrogen into usable nitrates.
8. Which of the following gases is NOT considered a primary greenhouse gas?
A. Carbon dioxide (CO₂)
B. Methane (CH₄)
C. Water Vapor
D. Nitrogen (N₂)
Answer: D. Nitrogen (N₂)
Explanation: Nitrogen gas does not trap infrared radiation. CO₂, CH₄, N₂O, and water vapor are key greenhouse gases responsible for the greenhouse effect.
9. Acid rain is primarily caused by elevated atmospheric levels of oxides of:
A. Carbon and Nitrogen
B. Sulfur and Nitrogen
C. Phosphorus and Sulfur
D. Carbon and Hydrogen
Answer: B. Sulfur and Nitrogen
Explanation: Burning fossil fuels releases SO₂ and NO₂, which react with atmospheric water vapor to form sulfuric and nitric acids, falling as acid rain.
10. The process of conversion of atmospheric nitrogen into nitrates and nitrites is called:
A. Nitrification
B. Nitrogen Fixation
C. Ammonification
D. Denitrification
Answer: B. Nitrogen Fixation
Explanation: Nitrogen fixation converts inert N₂ gas into biologically useful forms like nitrates and nitrites via biological or industrial processes.
This page contains a chapter-wise objective practice set. Try the questions without checking the answer first, then use the explanation to understand the point you missed. The current page contains 10 questions, so you can practise in smaller sets when you are revising.
Quick revision tip
After the practice set, write down the question numbers you missed and revise only those concepts once more. This makes MCQ practice more useful than repeatedly attempting the same questions without reviewing mistakes.
