CFC have a continuing effect on ozone layer as

The correct option is: "Cl atoms formed by them only act as catalysts in reactions causing degradation of ozone"

Chlorofluorocarbons (CFCs) are highly stable, synthetic organic compounds that drift slowly into the stratosphere. Once in the stratosphere, intense ultraviolet (UV) radiation breaks them down, releasing highly reactive chlorine (Cl) atoms.

These chlorine atoms initiate a chain reaction that breaks down ozone ($O_3$) molecules. The key to their long-lasting, devastating effect on the ozone layer lies in the catalytic nature of this process.
Let us look at the step-by-step chemical reactions involved:

1. Photodissociation of CFCs:
Under UV light, a CFC molecule releases a chlorine free radical:
$\mathrm{CF}{\mathrm{Cl}}_3+\mathrm{UV\; light}\to \mathrm{CF}{\mathrm{Cl}}_2+\mathrm{Cl}$

2. Ozone Destruction:
The chlorine atom reacts with ozone to form chlorine monoxide (ClO) and diatomic oxygen ($O_2$):
$\mathrm{Cl}+O_3\to \mathrm{ClO}+O_2$

3. Regeneration of Chlorine (Catalytic Cycle):
Chlorine monoxide then reacts with a free oxygen atom (O) in the stratosphere, releasing the chlorine atom back into its active form:
$\mathrm{ClO}+O\to \mathrm{Cl}+O_2$

Because the chlorine atom ($\mathrm{Cl}$) is regenerated at the end of the cycle, it is not consumed in the overall reaction. It acts strictly as a catalyst. A single chlorine atom can repeatedly cycle through these reactions, destroying tens of thousands of ozone molecules before it is eventually removed by other chemical processes or drifts out of the stratosphere. This explains why CFCs have a continuing, long-term destructive effect on the ozone layer.