UV rays act on chlorofluorocarbons (CFCs) and release __________ which degrades the ozone layer in the stratosphere.

The correct option is B $Cl$
The ozone layer present in the stratosphere acts as a shield as it absorbs the harmful UV radiation and prevents it from reaching the Earth's surface. But unfortunately, the ozone layer is getting depleted due to the pollutants such as chlorofluorocarbons (CFCs) released into the atmosphere due to human activities.

Ozone hole refers to the thinning of the stratospheric ozone layer which is clearly visible in the region of Antarctica. CFCs are commonly called ozone depleting substances.

Ozone gas is continuously formed and degraded in the atmosphere by the action of UV rays but the balance is lost due to the presence of ozone depleting substances.

CFCs are the most damaging agents of the ozone layer. They are widely used in refrigerants.

CFCs discharged in the lower part of the atmosphere move upwards to the stratosphere. Here they are acted upon by the UV radiation and free Cl atoms are released.

The active chlorine atoms catalytically destroy ozone by converting it into molecular oxygen.

Hence, option b is correct.