Concept:Ozone depletion is caused mainly by chlorofluorocarbons (CFCs) and is most severe over the Antarctic region.
Explanation:The ozone layer is a region in the stratosphere with a high concentration of
O3​ molecules that absorb most harmful ultraviolet (UV) radiation from the Sun.
The ozone hole refers to the thinning of this layer, observed primarily over the Antarctic.
The primary cause is the emission of CFCs and other ozone‑depleting substances.
When CFCs reach the stratosphere, UV light breaks them down, releasing chlorine atoms.
These chlorine atoms catalytically destroy ozone molecules.
During the long Antarctic winter, extremely cold temperatures allow polar stratospheric clouds (PSCs) to form.
PSCs provide surfaces for chemical reactions that convert inactive chlorine into active forms.
When sunlight returns in spring, these active chlorine compounds rapidly deplete ozone, creating the ozone hole.
International treaties like the Montreal Protocol (1987) have phased out CFCs, and the ozone layer is slowly recovering.
Scientists expect it to return to pre‑1980 levels by the mid‑21st century.
Answer:Option A: the Antarctic caused mainly by CFC gases.