Correct option: (b) (I) and (II) Only
In an pollution free stratosphere, the production and destruction of ozone are in balance and hence the concentration of O3 remains constant with time. When CFC’s are released into the lower troposphere, they diffuse up into the stratosphere since their lifetime is 50-100 years when CFCs reach the middle stratosphere, UV radiation liberates the chlorine atom.
CFC + UV → Cl
Cl is then able to destroy as man as 100,000 O3 molecules