What happens when UV radiation hits CFCs in the stratosphere?

• A. They sink to Earth's surface
• B. They release chlorine atoms that destroy ozone
• C. They become harmless
• D. They form ozone

Answer: (B)

UV radiation in the stratosphere breaks apart CFC molecules, releasing chlorine atoms. Those chlorine atoms start catalytic cycles that destroy ozone. A common sequence is Cl reacting with ozone to form ClO and O2, then ClO reacting with a free oxygen atom to regenerate Cl and produce more O2. The chlorine is reused, so one chlorine atom can destroy many ozone molecules. CFCs are long-lived in the upper atmosphere, so they persist long enough to cause this depletion. They don’t sink to Earth or become harmless on their own, and they don’t form ozone; they reduce ozone instead.