The correct answer is (b) thinning of the ozone layer.
Explanation:
An “ozone hole” refers to a region in the atmosphere where the concentration of ozone has significantly decreased, causing a thinning of the ozone layer, not a literal hole.
Why other options are incorrect:
(a) a large sized hole in the ozone layer:
While the term “hole” is used metaphorically, the ozone hole is not a physical hole with no ozone present. It’s a region with a significantly reduced amount of ozone.
(c) small holes scattered in the ozone layer:
The ozone hole is not characterized by small holes scattered throughout the ozone layer. It’s a localized area of depletion, usually over Antarctica.
(d) thickening of ozone in the ozone layer:
The ozone hole represents the opposite of thickening. Thickening of the ozone layer would be a positive development in terms of protecting the Earth from harmful UV radiation, but the term “ozone hole” specifically refers to its thinning.