Which category is a classic ozone-depleting substance?

Which category is a classic ozone-depleting substance?

• A. Carbon dioxide
• B. Chlorofluorocarbons (CFCs)
• C. Oxygen
• D. Argon

Answer: (B)

The main idea is understanding which chemicals in common use actually break down the ozone layer in the upper atmosphere. Ozone in the stratosphere protects us from harmful UV radiation, and certain human-made compounds can reach there and release reactive atoms when exposed to UV light. Chlorofluorocarbons are a classic example. They are very stable at Earth’s surface, so they ride up into the stratosphere unchanged. There, UV photons break them apart to release chlorine atoms. Those chlorine atoms kick off catalytic cycles that destroy ozone: a chlorine atom reacts with ozone to form ClO and O2, then the ClO reacts with a second oxygen atom to release another O2 and regenerate the chlorine atom. Because chlorine acts as a catalyst, a single molecule can destroy many ozone molecules over time. Other options don’t fit this mechanism. Carbon dioxide is a greenhouse gas affecting climate, not a primary ozone-depleting agent. Oxygen is the essential molecule we breathe and doesn’t act to destroy ozone. Argon is an inert noble gas with no reactivity to drive ozone loss. So, the classic ozone-depleting substance is chlorofluorocarbons.

The main idea is understanding which chemicals in common use actually break down the ozone layer in the upper atmosphere. Ozone in the stratosphere protects us from harmful UV radiation, and certain human-made compounds can reach there and release reactive atoms when exposed to UV light.

Chlorofluorocarbons are a classic example. They are very stable at Earth’s surface, so they ride up into the stratosphere unchanged. There, UV photons break them apart to release chlorine atoms. Those chlorine atoms kick off catalytic cycles that destroy ozone: a chlorine atom reacts with ozone to form ClO and O2, then the ClO reacts with a second oxygen atom to release another O2 and regenerate the chlorine atom. Because chlorine acts as a catalyst, a single molecule can destroy many ozone molecules over time.

Other options don’t fit this mechanism. Carbon dioxide is a greenhouse gas affecting climate, not a primary ozone-depleting agent. Oxygen is the essential molecule we breathe and doesn’t act to destroy ozone. Argon is an inert noble gas with no reactivity to drive ozone loss.

So, the classic ozone-depleting substance is chlorofluorocarbons.