In stratosphere, which of the following elements acts as a catalyst in degradation of ozone and release of molecular oxygen?

In stratosphere, Cl acts as a catalyst in degradation of ozone and release of molecular oxygen. CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, UV rays act on them releasing Cl atoms. Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts; Cl atoms are not consumed in the reaction. Hence, whatever CFCs are added to the stratosphere, they have permanent and continuing effects on Ozone levels.