Question

About 20 km above the earth, there is an ozone layer. Which one of the following statements about ozone and ozone layer is true?

• A. Ozone is a triatomic linear molecule
• B. It is harmful as it stops useful radiation
• C. It is beneficial to us as it stops UV-radiation
• D. Conversion of $O_3 \, to \, O_2$ is an endothermic reaction

Answer 1

Answer: (C)

It is beneficial to us as it stops UV-radiation

Answer 2

Ozone is an allotropic form of oxygen. It is
present in the upper atmosphere (about 20 km
above the surface of the earth). It is believed to be
formed in the upper atmosphere by the action of
UV-rays on oxygen as
$\, \, \, \, \, \, 3O_2 \, + \, UV-rays \longrightarrow \, 2O_3,$
$\, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \Delta H = 142.7 kJ \, mol^{-1}$
Therefore, UV-rays, which are harmful to human
beings are absorbed by oxygen to form ozone. The
layer of ozone, thus formed also prevents the
remaining UV-rays to reach the earth- surface.