MPSC Previous Year Questions (PYQ)
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1. Which gas is a major contributor to global warming?
(A) Oxygen
(B) Carbon dioxide
(C) Nitrogen
(D) Argon
Answer: (B) Carbon dioxide
Explanation: CO₂ is an important greenhouse gas that absorbs outgoing infrared radiation.
2. Which of the following is a greenhouse gas?
(A) Oxygen
(B) Nitrogen
(C) Methane
(D) Helium
Answer: (C) Methane
Explanation: Methane (CH₄) is a potent greenhouse gas.
3. The major cause of acid rain is the emission of:
(A) Oxygen and hydrogen
(B) Sulphur dioxide and nitrogen oxides
(C) Carbon monoxide and methane
(D) Nitrogen and oxygen
Answer: (B) Sulphur dioxide and nitrogen oxides
Explanation: SO₂ and nitrogen oxides react in the atmosphere to form acids that contribute to acid rain.
4. Acid rain generally has a pH:
(A) Above 7
(B) Equal to 7
(C) Below 5.6
(D) Exactly 14
Answer: (C) Below 5.6
Explanation: Natural rain is slightly acidic, around pH 5.6, mainly because CO₂ dissolves in water. Acid rain is more acidic than this.
5. Which gas is primarily responsible for the formation of acid rain from sulphur-containing fuels?
(A) Sulphur dioxide
(B) Oxygen
(C) Hydrogen
(D) Helium
Answer: (A) Sulphur dioxide
6. Which atmospheric layer contains the highest concentration of ozone?
(A) Troposphere
(B) Stratosphere
(C) Mesosphere
(D) Thermosphere
Answer: (B) Stratosphere
7. The ozone layer protects life on Earth mainly by absorbing:
(A) Infrared radiation
(B) Ultraviolet radiation
(C) Radio waves
(D) Sound waves
Answer: (B) Ultraviolet radiation
8. Which group of chemicals was historically a major cause of stratospheric ozone depletion?
(A) CFCs
(B) Carbonates
(C) Chlorides in seawater
(D) Nitrates
Answer: (A) CFCs
Explanation: Chlorofluorocarbons release chlorine radicals in the stratosphere that catalytically destroy ozone.
9. Which of the following is a major air pollutant produced by incomplete combustion of fuels?
(A) Carbon monoxide
(B) Oxygen
(C) Nitrogen
(D) Water vapour
Answer: (A) Carbon monoxide
10. Carbon monoxide is particularly dangerous because it:
(A) Increases the oxygen-carrying capacity of blood
(B) Combines strongly with haemoglobin and reduces oxygen transport
(C) Converts oxygen into nitrogen
(D) Prevents water evaporation
Answer: (B) Combines strongly with haemoglobin and reduces oxygen transport
11. Photochemical smog is formed mainly through reactions involving:
(A) Nitrogen oxides and volatile organic compounds in sunlight
(B) Oxygen and nitrogen in darkness
(C) Water vapour and helium
(D) Carbon dioxide and hydrogen
Answer: (A) Nitrogen oxides and volatile organic compounds in sunlight
12. Which pollutant is a major component of photochemical smog?
(A) Ground-level ozone
(B) Oxygen
(C) Nitrogen
(D) Water vapour
Answer: (A) Ground-level ozone
13. Smog is best described as:
(A) Pure water vapour
(B) A mixture of air pollutants producing hazy atmospheric conditions
(C) Pure oxygen
(D) A layer of nitrogen
Answer: (B) A mixture of air pollutants producing hazy atmospheric conditions
14. Which of the following is a major cause of water pollution?
(A) Untreated sewage
(B) Oxygen
(C) Rainwater
(D) Nitrogen in the atmosphere
Answer: (A) Untreated sewage
15. Excessive nutrients such as nitrates and phosphates entering water bodies can cause:
(A) Eutrophication
(B) Sublimation
(C) Condensation
(D) Distillation
Answer: (A) Eutrophication
Explanation: Excess nutrients promote excessive algal growth, which can reduce dissolved oxygen and harm aquatic life.
16. Which water pollutant is commonly associated with industrial discharge and can be toxic even at low concentrations?
(A) Heavy metals
(B) Oxygen
(C) Nitrogen gas
(D) Hydrogen
Answer: (A) Heavy metals
17. Which of the following is a primary pollutant?
(A) Carbon monoxide
(B) Ozone formed in the atmosphere
(C) Photochemical smog
(D) Sulphuric acid formed in clouds
Answer: (A) Carbon monoxide
Explanation: A primary pollutant is emitted directly from a source. Carbon monoxide is directly emitted during incomplete combustion.
18. Which of the following is a secondary pollutant?
(A) Carbon monoxide emitted from vehicles
(B) Sulphur dioxide emitted from a factory
(C) Ground-level ozone formed through atmospheric reactions
(D) Dust released from construction
Answer: (C) Ground-level ozone
19. Global warming refers primarily to:
(A) Long-term increase in Earth’s average surface temperature
(B) Daily variation in temperature
(C) Cooling of the oceans only
(D) Increase in atmospheric oxygen
Answer: (A) Long-term increase in Earth’s average surface temperature
20. Which of the following correctly matches the environmental problem with its major cause?
(A) Acid rain — SO₂ and NOₓ
(B) Ozone depletion — CFCs
(C) Global warming — Greenhouse gases
(D) All of the above
Answer: (D) All of the above
Quick Revision — Environmental Chemistry
| Topic | Must Remember |
|---|---|
| Global warming | Long-term rise in Earth’s average temperature |
| Greenhouse gases | CO₂, CH₄, N₂O, water vapour, etc. |
| Acid rain | Mainly SO₂ + NOₓ |
| Acid rain pH | Below about 5.6 |
| Ozone layer | Stratosphere |
| Ozone function | Absorbs harmful UV radiation |
| Ozone depletion | Historically associated strongly with CFCs |
| CO | Dangerous because it binds haemoglobin strongly |
| Photochemical smog | NOₓ + VOCs + sunlight |
| Ground-level ozone | Secondary pollutant |
| Water pollution | Sewage, industrial waste, agricultural runoff |
| Eutrophication | Excess nutrients → algal growth → oxygen depletion |
| Heavy metals | Toxic water pollutants |
| Primary pollutant | Emitted directly |
| Secondary pollutant | Formed in atmosphere by reactions |