Ozone is a molecule containing three atoms of oxygen (O3), a highly poisonous gas present in the upper layer of the atmosphere.
Formation of Ozone : The UV radiations split molecular oxygen (O2) apart into free oxygen atoms (O + O). These atoms then combine with molecular oxygen to form ozone.
O2 → O + O ,O + O2 → O3
Effect : Ozone layer shields the surface of the earth from damaging UV radiations of the sun.