The gas $A$ has very low reactivity and reaches the stratosphere. It is non-toxic and non-flammable but is dissociated by $UV$ radiations in the stratosphere. The intermediates formed initially from the gas $A$ are:

• A
  $Cl\dot{O} + \dot{CF_2}Cl$
• B
  $Cl\dot{O} + \dot{C}H_3$
• C
  $\dot{C}H_3 + \dot{CF_2}Cl$
• D
  $\dot{Cl} + \dot{CF_2}Cl$