State how CFCs break ozone layer.

CFCs are decomposed by ultra-violet rays to highly reactive chlorine, which is produced in its atomic form.

CF₂Cl₂ (g) $\xrightarrow {\text{Ultraviolet rays}}$ CF₂Cl (g) + Cl (g) [free radical]

This free radical [Cl] reacts with ozone forming chlorine monoxide.

Cl(g) + O₃(g) ⟶ ClO (g) + O₂ (g)

This causes depletion of ozone, and chlorine monoxide further reacts with atomic oxygen to produce more free radicals of chlorine.

ClO (g) + O (g) ⟶ Cl (g) + O₂ (g)

Again this free radical [Cl] destroys ozone, and the process continues, giving rise to large scale ozone depletion.