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 answer
Explanation
The correct answer is A, the Antarctic caused mainly by CFC gases. The ozone hole is a sharp seasonal thinning of the stratospheric ozone layer over Antarctica, caused mainly by chlorine from chlorofluorocarbons.
CFCs, once used in refrigerators, air conditioners and aerosol sprays, rise to the stratosphere, where ultraviolet light breaks them down and frees chlorine atoms; a single chlorine atom can destroy thousands of ozone molecules. Over Antarctica, the extreme cold forms polar stratospheric clouds, on which this reaction speeds up when sunlight returns in spring (September to November). The hole was reported by British scientists in 1985, which led to the Montreal Protocol of 1987 to phase out ozone-depleting substances.
B is wrong: carbon dioxide is a greenhouse gas that causes global warming; it does not destroy ozone.
C is wrong: the Arctic also loses some ozone, but the deep annual hole forms over the Antarctic, which is colder.
D is wrong: both the place and the cause are wrong.
Exam tip: ozone hole = Antarctic spring, CFCs (chlorine), Montreal Protocol 1987; World Ozone Day is 16 September; ozone is measured in Dobson units.
Practice Questions
View allWhich one of the following statements with regard to growth of coral reefs is not correct?
- A.Coral can grow abundantly in freshwater.
- B.It requires warm water between 23 °C-25 °C.
- C.It requires shallow saltwater, not deeper than 50 metres.
- D.It requires plenty of sunlight to aid photosynthesis.
Show answer
Reef-building corals are marine animals and die in fresh water, so this statement is false. Corals are tiny polyps that build skeletons of calcium carbonate and live with algae called zooxanthellae inside their tissues.
Read the full explanation →Which one of the following biosphere reserves is spread over three States in India?
- A.Nilgiri
- B.Achanakmar-Amarkantak
- C.Seshachalam
- D.Agasthyamalai
Show answer
The Nilgiri Biosphere Reserve spreads across Tamil Nadu, Kerala and Karnataka. Set up in 1986, Nilgiri was India's first biosphere reserve, and in 2000 it became the first Indian reserve on UNESCO's World Network of Biosphere Reserves.
Read the full explanation →Which of the following is/are renewable source(s) of energy? 1. Fossil fuel 2. Biofuel 3. Uranium 4. Hydropower Select the correct answer using the code given below.
- A.2 only
- B.3 and 4
- C.1 and 3
- D.2 and 4
Show answer
Biofuel and hydropower are renewable because nature replaces them within a human lifetime, while fossil fuels and uranium are not.
Read the full explanation →Which one of the following is NOT decomposed by bacterial action ?
- A.Vegetable remains
- B.Plastic materials
- C.Animal carcasses
- D.Wastes of flowers
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Ordinary plastics are non-biodegradable, so bacteria and fungi cannot break them down in any useful length of time. Most plastics, such as polyethylene, polypropylene and PVC, are long synthetic polymers made from petroleum.
Read the full explanation →According to the Environmental Protection Agency (EPA), which one of the following is the largest source of sulphur dioxide emissions?
- A.Locomotives using fossil fuels
- B.Ships using fossil fuels
- C.Extraction of metals from ores
- D.Power plants using fossil fuels
Show answer
The EPA names the burning of fossil fuels by power plants and other industrial facilities as the largest source of sulphur dioxide.
Read the full explanation →