Ozone hole is a region over :
- (a)the Antarctic caused mainly by CFC gases.
- (b)the Antarctic caused mainly by carbon dioxide gas.
- (c)the Arctic caused mainly by CFC gases.
- (d)the Arctic caused mainly by carbon dioxide gas.
Correct — A, the Antarctic caused mainly by CFC gases. The hole is a springtime thinning of stratospheric ozone over Antarctica, and the agent is chlorine released from chlorofluorocarbons, not carbon dioxide.
- (b)the Antarctic caused mainly by carbon dioxide gas. — Carbon dioxide is a greenhouse gas; it warms the troposphere but does not catalytically destroy ozone. The chemistry that thins the ozone layer is chlorine- and bromine-driven.
- (c)the Arctic caused mainly by CFC gases. — The Arctic does thin in some years, but it has never formed the deep, recurring hole seen over Antarctica — the polar vortex there is warmer and less stable, so fewer polar stratospheric clouds form.
- (d)the Arctic caused mainly by carbon dioxide gas. — Wrong on both counts: wrong pole and wrong gas.
Stratospheric ozone is destroyed catalytically by chlorine atoms freed from CFCs by ultraviolet light, and the reaction runs fastest on the surfaces of polar stratospheric clouds, which need the extreme cold of the Antarctic winter vortex.
One chlorine atom can destroy many thousands of ozone molecules before it is locked away, which is why a small mass of CFC has such a large effect. The Montreal Protocol (1987) phased CFCs out, and the Antarctic hole has been measurably shrinking since about 2000 — anchored to the 2024 exam, the layer is projected to recover to 1980 levels around 2066 over Antarctica.
- The hole appears each Antarctic spring (September-October), not year-round.
- Chlorine from CFCs is the main agent; bromine from halons contributes.
- Polar stratospheric clouds provide the surfaces the reaction needs, so the deep hole is an Antarctic phenomenon.
- Ozone depletion and global warming are distinct problems with distinct gases.
The commonest trap in this topic is swapping the two gases.
- Attributing the ozone hole to carbon dioxide.
- Placing the hole over the Arctic.
- Assuming the hole is permanent rather than seasonal.
Almost always as a single-line identification pairing a pole with a gas — get the pairing right and the item falls immediately.
No directly related past PYQ was found.
- practice — not a real PYQ
The Montreal Protocol, which phased out ozone-depleting substances, was adopted in
- (a)1985
- (b)1987
- (c)1992
- (d)1997
Answer(b) 1987 — the Vienna Convention was 1985; the Kyoto Protocol was 1997.