Which molecule destroys the ozone layer?

• A. Oxygen
• B. Hydrogen
• C. Chlorine
• D. Carbon dioxide

Answer: (C)

Ozone depletion in the stratosphere happens through catalytic cycles that involve halogen atoms, with chlorine as the main destroyer. A chlorine atom reacts with ozone to form chlorine monoxide and oxygen: Cl + O3 → ClO + O2. The ClO then reacts with a free oxygen atom to regenerate chlorine and produce more O2: ClO + O → Cl + O2. The chlorine atom is regenerated and can continue this process, so one chlorine atom can destroy many ozone molecules, thinning the ozone layer.

Oxygen itself is a building block of ozone, not a net destroyer in this catalytic cycle, and carbon dioxide does not participate in this ozone-destroying mechanism in the same way. Hydrogen can be involved in other reactive pathways, but chlorine from human-made compounds is the primary agent linked to the observed depletion.