List the importance of oxygen gas and ozone gas present in the atmosphere.

(N/A) $O_2$ gas: Essential for respiration in living organisms,supports combustion,and is involved in the formation of oxides of nitrogen.
$O_3$ gas: Acts as a protective shield in the stratosphere by absorbing harmful ultraviolet $(UV)$ radiations from the sun,which prevents them from reaching the Earth's surface and causing damage to living organisms.