Science (086) — AI-generated practice question

A chemical being non-reactive and non-toxic at ground level does not guarantee environmental safety because its behaviour can change drastically at higher levels of the atmosphere.

CFCs are stable and harmless near the ground, but when they rise to the upper atmosphere, UV radiation breaks them down, releasing chlorine atoms that deplete the ozone layer. The ozone layer shields Earth from harmful UV radiation, which causes skin cancer and damages organisms.

Therefore, a chemical must be evaluated for its effects throughout the entire atmosphere and ecosystem, not just at ground level.

Source: Chapter 13, Section 13.2.1 — Ozone Layer and How it is Getting Depleted

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• The examiner wants you to connect ground-level stability of CFCs → upper atmosphere behaviour → ozone depletion → UV damage. These are the three logical steps worth the 3 marks.
• Mention the specific harm (UV radiation, skin cancer) to show you understand why ozone depletion matters.
• Don't just say "CFCs are bad" — explain the mechanism: UV breaks CFCs apart at higher altitude, and they then destroy ozone.
• The UNEP/1987 agreement is useful background but not required for this specific question.