CAPF AC 2023 Q32: Environment & Ecology – Pollution & Waste Management
- (a) chlorofluorocarbon
- (b) carbon monoxide
- (c) methane
- (d) pesticides
Answer: (a) chlorofluorocarbon
Explanation
What thinned the ozone layer
How to think: ask which substance is a stable gas that rises to the stratosphere and is broken by sunlight there.
Only one option fits: the chlorine in chlorofluorocarbons (CFCs).
| Option | Where it is used | Effect on ozone |
|---|---|---|
| Chlorofluorocarbons | Refrigerators, air conditioners, aerosol sprays, foam | Release chlorine in the stratosphere, which destroys ozone |
| Carbon monoxide | Vehicle exhaust | Poisonous gas, not an ozone destroyer |
| Methane | Paddy fields, cattle, marshes | A greenhouse gas |
| Pesticides | Farms | Pollute soil and water |
Chain of events: UV light breaks a CFC molecule, one chlorine atom is freed, and that single atom can break down thousands of ozone molecules.
The loss is seen as the ozone hole over Antarctica each spring.
Answer: (a) chlorofluorocarbon.
Why each option is right or wrong
- (a) CORRECT. CFCs release chlorine, which breaks down ozone in the stratosphere.
- (b) Incorrect. Carbon monoxide is a toxic gas from burning fuel and does not thin the ozone layer.
- (c) Incorrect. Methane is a greenhouse gas that adds to warming, not to ozone loss.
- (d) Incorrect. Pesticides harm soil, water and living things, not the ozone layer.
Key point
CFCs: used in refrigeration, air conditioning, aerosols and foam; chlorine atom breaks ozone (O3) into O2. Montreal Protocol, 1987: phases out ozone-depleting substances. Ozone layer lies in the stratosphere (15-35 km) and absorbs UV-B.
Remember
Ozone layer thinned by CFCs; the Montreal Protocol (1987) is the treaty.
Common mistakes
- Confusing ozone depletion (CFCs) with global warming (carbon dioxide and methane).
- Choosing carbon monoxide because it is a well-known pollutant gas.
- Forgetting that the ozone layer sits in the stratosphere, not at ground level.
Exam tip
Educated guess: 'Ozone' and 'CFC' are always paired in the news, so the two words should lead you straight to (a). The other three are pollutants with a different problem.
Sources
- NCERT Class XII Biology — Environmental Issues, Chapter 16 (ozone depletion in the stratosphere)
- UNEP, The Montreal Protocol on Substances that Deplete the Ozone Layer (1987)