The correct answer is A. chlorine.
CFCs (chlorofluorocarbons) are a group of chemicals that were once widely used in refrigerants, aerosol propellants, and foam-blowing agents. They are very stable and do not react with most things, but they do react with ozone in the stratosphere. When CFCs reach the stratosphere, they are broken down by ultraviolet radiation, releasing chlorine atoms. These chlorine atoms then react with ozone molecules, destroying them.
Chlorine is the most important chemical that destroys ozone. It is estimated that one chlorine atom can destroy up to 100,000 ozone molecules.
Fluorine is also a component of CFCs, but it does not react with ozone. Nitrogen dioxide (N2O) and sulfur dioxide (SO2) are other chemicals that can destroy ozone, but they are not as important as chlorine.
CFCs were banned in the 1980s because of their harmful effects on the ozone layer. However, they remain in the atmosphere for a long time, and they will continue to destroy ozone for many years to come.