The thickness of ozone in a column of air in the atmosphere is measured in terms of:

Assertion : $UV$ radiation causes photodissociation of ozone into $O_2$ and $O$,thus causing damage to the stratospheric ozone layer.
Reason : Ozone hole is resulting in global warming and climate change

Why is an ozone hole formed over Antarctica?

What is the result of the action of ultraviolet $(UV)$ rays on molecular oxygen $(O_2)$?

The presence of ozone $(O_3)$ in the atmosphere of Earth:

The result of the ozone hole is: