State one important function of ozone layer in the atmosphere. How is it formed there? Which compounds are responsible for the depletion of ozone layer? How do these compounds enter into the atmosphere?

(N/A) The ozone layer in the upper atmosphere acts as a shield by protecting living organisms from harmful $UV$ radiations.
Formation of ozone layer:
Ozone at higher levels of the atmosphere is formed by the action of $UV$ radiations on oxygen $(O_2)$ molecules. High-energy $UV$ radiations split molecular oxygen $(O_2)$ into free oxygen $(O)$ atoms. These atoms then combine with molecular oxygen to form ozone $(O_3)$:
$O_2 \xrightarrow{UV} O + O$
$O + O_2 \longrightarrow O_3$
Compounds responsible for depletion:
Chlorofluorocarbons $(CFCs)$ are the primary compounds responsible for the depletion of the ozone layer.
Entry into the atmosphere:
These compounds enter the atmosphere through human-made sources such as aerosol sprays,refrigerants in refrigerators,air conditioners,and fire extinguishers that utilize $CFCs$.