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 beneficial to us as it stops U.V. radiation.
(b) Conversion of O3 to O2 is an endothermic reaction.
(c) Ozone has a triatomic linear molecule.
(d) It is harmful as it stops useful radiation.
