Questions & Answers

Ozone hole is caused by
A. Acetylene
B. Ethylene
C. Chlorofluorocarbons
D. Methane

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Hint: In an ecosystem, all the biotic (living factors) and abiotic (non-living factors) components interact with each other. This interaction is always inter-related, interdependent and mutually reactive in a balanced and healthy ecosystem. Thus the ecosystem is referred to as the self-regulatory and self-sustaining functional and structural unit of nature. All the organisms present in an ecosystem (visible or not) have a definite role to play in maintaining the balance of the ecosystem.

Complete answer:
The accelerated rates of species extinctions are largely due to human activities. The major causes for the accelerated biodiversity loss are habitat loss and fragmentation or deforestation. Due to deforestation, the area covered by rainforests decreased so severely that the water cycle of the earth is disturbed to a large extent.
A higher concentration of carbon dioxide forms a thick layer above the earth's surface, checking the radiation of the heat from the earth surface. Because of this, the temperature of the earth's surface increases, this is called global warming.
Ozone is present in less quantity in the atmosphere. But at a particular height on earth, the concentration of ozone is maximum in the stratosphere.
The aerosols like CFCs or the chlorofluorocarbons released into the atmosphere from the refrigerators, air conditioners and jet planes deplete or reduce the ozone layer. This is called ozone depletion and these substances are called ozone-depleting substances. The thin layer of ozone is called an ozone hole.

Hence, the correct answer is option (C).

Note: Due to the depletion of the ozone layer, harmful UV radiations are penetrating to the earth, which causes skin cancer (melanoma) and also acts as strong mutagens. The shorter wavelengths of UV radiations are completely absorbed by the earth's atmosphere if the ozone layer is intact. But higher wavelengths damage the DNA and mutation may occur.