CBSE Class 10 Science 2020 · Paper 31/3/3 · Question 18(b)

Formation: high in the atmosphere, UV radiation from the Sun splits some oxygen molecules into free oxygen atoms, ${\text{O}}_2\stackrel{\text{UV}}{\to }\text{O}+\text{O}$; these atoms then combine with oxygen molecules to form ozone, $\text{O}+{\text{O}}_2⟶{\text{O}}_3$. Importance: the ozone layer absorbs most of the harmful ultraviolet radiation from the Sun, so it protects all life forms on earth from its harmful effects, such as skin cancer in human beings. Fall in the 1980s: synthetic chemicals like chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers, were released into the atmosphere and broke down the ozone.