(N/A) In the stratosphere,ozone is formed by the action of $UV$ radiation on dioxygen as:
$(i) \, O_{2(g)} \xrightarrow{UV} O_{(g)} + O_{(g)}$
$(ii) \, O_{2(g)} + O_{(g)} \rightarrow{UV} O_{3(g)}$
Reaction $(ii)$ indicates the dynamic equilibrium existing between the production and decomposition of ozone molecules. Any factor that disturbs this equilibrium may cause depletion of the ozone layer. One such factor is the release of chlorofluorocarbon compounds $(CFCs)$. These are non-reactive,non-flammable molecules used in refrigerators,air conditioners,plastics,and electronic industries.
Once released,$CFCs$ mix with atmospheric gases and reach the stratosphere,where they are decomposed by $UV$ radiation:
$(iii) \, CF_{2}Cl_{2(g)} \xrightarrow{UV} \dot{Cl}_{(g)} + \dot{C}F_{2}Cl_{(g)}$
The chlorine free radical produced in reaction $(iii)$ reacts with ozone as:
$(iv) \, \dot{Cl}_{(g)} + O_{3(g)} \to Cl\dot{O}_{(g)} + O_{2(g)}$
$(v) \, Cl\dot{O}_{(g)} + O_{(g)} \to \dot{Cl}_{(g)} + O_{2(g)}$
The regeneration of $\dot{Cl}_{(g)}$ radicals causes a continuous breakdown of ozone present in the stratosphere,leading to the depletion of the ozone layer.