Identify Gas A. How is it formed at higher levels of the atmosphere?

13 Gas A, found in the upper layers of the atmosphere, is a deadly poison but is essential for all living beings. The amount of this gas started declining sharply in the 1980s.
a. Identify Gas A. How is it formed at higher levels of the atmosphere?

Ans : a. Gas A is Ozone. Alternatively accept the formula of the gas.
Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms then combine
with molecular oxygen to form ozone.
Alternatively accept the following equations with the correct molecular formulae. No mark to be assigned if molecular formulae are not correct, when only the equation is written.