CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 9(b)

Formation: In the upper atmosphere, high-energy ultraviolet (UV) radiation from the Sun splits some oxygen molecules into free oxygen atoms, which then combine with molecular oxygen to form ozone: ${\text{O}}_2\stackrel{\text{UV}}{\to }\text{O}+\text{O}$; $\text{O}+{\text{O}}_2\to {\text{O}}_3$. Importance: The ozone layer shields the surface of the Earth from the harmful ultraviolet radiation of the Sun by absorbing it. Depletion: Chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers and aerosol sprays, are responsible for the depletion of ozone. Harmful effect: More UV radiation reaches the Earth and causes skin cancer in human beings (it can also cause cataract and eye damage, and weaken the immune system).