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

Answer 1

The correct option is B It is beneficial to us as it stops UV-radiation

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
$3O_2+\text{UV-rays}\to 2O_3;\Delta H=142.7kJ/mol$
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.
Option (c) is correct.