Which one of the following is mainly responsible for the depletion of the ozone layer?

Chlorofluorocarbons

The correct answer is (3) chlorofluorocarbons (CFCs).

CFCs are man-made chemicals that are used in a variety of products, including refrigerators, air conditioners, and foam insulation. When CFCs are released into the atmosphere, they break down under the influence of ultraviolet radiation from the sun. This releases chlorine atoms, which react with ozone molecules in the stratosphere, destroying them.

The other options are incorrect. Option (1), water, is not a major factor in ozone depletion. Option (2), carbon dioxide, is a greenhouse gas, but it does not directly destroy ozone molecules. Option (4), methane, is also a greenhouse gas, but it does not directly destroy ozone molecules.

Therefore, the main factor responsible for the depletion of the ozone layer is the release of CFCs into the atmosphere.