What molecule destroys ozone?

• A. Oxygen
• B. Nitrogen
• C. Hydrogen
• D. Chlorine

Answer: (D)

Ozone is destroyed through catalytic cycles in the stratosphere, with chlorine playing the key role. When chlorine atoms meet ozone, they form chlorine monoxide and oxygen: Cl + O3 → ClO + O2. The ClO can then react with atomic oxygen to regenerate the chlorine atom and produce another molecule of O2: ClO + O → Cl + O2. Because the chlorine atom is regenerated, one chlorine atom can destroy many ozone molecules over time, making it a very effective ozone-depleting catalyst. This is why chlorine from human-made compounds like CFCs becomes potent ozone destroyers after being broken down by UV light in the upper atmosphere. Oxygen, nitrogen, and hydrogen don’t participate in this highly efficient catalytic cycle to the same extent in the stratosphere, so chlorine is the best answer here.