Dobson units $(DU)$ are used to measure the thickness of:

Which of the following statement$(s)$ is/are correct?
$(i)$ The Montreal Protocol was signed in $1987$ and became effective in $1989$.
$(ii)$ 'Good' ozone is found in the troposphere.
$(iii)$ Ozone is formed by the action of $UV$ rays on molecular oxygen and degrades into molecular oxygen.
$(iv)$ $CFCs$ are responsible for the imbalance between the production and degradation of ozone.
$(v)$ $DNA$ and proteins of living organisms absorb $UV$ rays.

The result of the ozone hole is:

The ozone hole is largest over $.......$.

Select the relevant option regarding the $Montreal$ $Protocol$.

Assertion $(A)$: Chlorofluorocarbons are responsible for ozone depletion.
Reason $(R)$: Ozone level decreases by as much as $67\%$ every year.