CBSE Class 10 Science 2022 · Paper 31/1/1 · Question 7(a)

Ozone is a molecule made of three atoms of oxygen, ${\text{O}}_3$. Formation: at the higher levels of the atmosphere, high-energy ultraviolet (UV) radiation from the Sun splits some oxygen molecules into free oxygen atoms, ${\text{O}}_2\stackrel{\text{UV}}{\to }\text{O}+\text{O}$; each free oxygen atom then combines with a molecule of oxygen to form ozone, $\text{O}+{\text{O}}_2\to {\text{O}}_3$. Effect on our ecosystem: the ozone layer shields the surface of the Earth from the Sun's ultraviolet radiation, which is highly damaging to organisms (it causes skin cancer in human beings, for example). By absorbing most of this radiation, ozone in the upper atmosphere protects the plants, animals and human beings of the ecosystem; where the layer has been depleted by chlorofluorocarbons (CFCs), more ultraviolet radiation reaches them. Near the ground, however, ozone is a deadly poison.