Assertion : UV radiation causes photodissociation of ozone into O_2...

Stratosphere zone of earth's atmosphere contains a layer of ozone $\left(\mathrm{O}_3\right)$ which prevents the earth surface from about $99 \%$ of incoming solar ultra violet radiations. The primary chemicals responsible for ozone depletion are a group of chlorine containing compounds called chloroflourocarbons (CFCs) used as coolants in refrigerators and air conditioners and propellants for aerosol cans and foam blowing agents for insulation and packaging and also as solvents. After their release into troposphere CFCs go to stratosphere when these are broken down by ultraviolet radiations releasing chlorine or bromine which break $\mathrm{O}_3$ molecules into $\mathrm{O}_2$ and $\mathrm{O}$. Due to depletion of $\mathrm{O}_3$ layer, higher levels of ultra violet rays reach earth surface. Depletion in the concentration of ozone over a restricted area is called ozone hole. Ozone depletions results in problems like skin cancer, cataract animals becoming blind, mutations, inhibiting photosynthesis, decreases in productivity. Decreased photosynthetic activity will increase $\mathrm{O}_2$ concentration of the atmosphere resulting in global warming. Besides $\mathrm{CFCs}$, nitrogen oxide and hydrocarbons are also responsible for $\mathrm{O}_3$ depletion.