(a) Why is the fluorine present in chlorofluorocarbons not a major contributor to depletion of the ozone layer? (b) What are the chemical forms in which chlorine exists in the stratosphere following cleavage of the carbon-chlorine bond?

Fluorine in chlorofluorocarbons (CFCs) forms strong covalent bonds with carbon atoms. Due to the strength of these bonds, they do not readily break down in the atmosphere. Instead, it's the weaker carbon-chlorine bonds in CFCs that are more susceptible to breakdown due to ultraviolet (UV) radiation. Upon breakdown, the released chlorine atoms react with ozone molecules, leading to the depletion of the ozone layer. Thus, the fluorine in CFCs remains relatively inert and does not have a significant impact on the ozone layer.

When the carbon-chlorine bond in a CFC molecule is cleaved by ultraviolet radiation, it releases a chlorine atom: \[CFCl_3 + \text{UV radiation} \rightarrow CFCl_2 + Cl\] The released chlorine atom then reacts with an ozone molecule, depleting the ozone layer by forming chlorine monoxide and molecular oxygen: \[Cl + O_3 \rightarrow ClO + O_2\] The chlorine monoxide (ClO) can react with another ozone molecule, forming more molecular oxygen and a chlorine atom: \[ClO + O_3 \rightarrow Cl + 2O_2\] The chlorine atom generated in this step can continue the process, causing further depletion of the ozone layer. In summary, once the carbon-chlorine bond is cleaved, the chemical forms of chlorine that exist in the stratosphere are primarily chlorine atom (Cl) and chlorine monoxide (ClO). The chlorine atom acts as a catalyst, leading to significant ozone depletion.