CBSE Class 10 Science 2022 · Paper 31(B)/6 · Question 8(a)

Formation: at the higher levels of the atmosphere, high-energy ultraviolet (UV) radiation from the Sun splits some oxygen molecules into free oxygen atoms, ${\text{O}}_2\stackrel{\text{UV}}{\to }\text{O}+\text{O}$, and each free atom combines with an oxygen molecule to form ozone, $\text{O}+{\text{O}}_2\to {\text{O}}_3$. Function: this ozone absorbs most of the harmful UV radiation from the Sun and so shields the surface of the Earth from it. UV radiation is highly damaging to organisms; for example, it is known to cause skin cancer in human beings. Steps taken: the fall was linked to synthetic chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers. In 1987 the United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels, and, as NCERT notes, it is now mandatory for manufacturers throughout the world to make CFC-free refrigerators.