Answer: Release chlorine radicals that catalytically destroy the ozone layer.
- A React with atmospheric water vapour to generate hydrochloric acid directly
- B Release chlorine radicals that catalytically destroy the ozone layer
- C Are acutely toxic to humans even at very low inhaled concentrations
- D Dissolve readily in rainwater, directly causing acid rain over cities
Correct answer: B. Release chlorine radicals that catalytically destroy the ozone layer
Explanation: Freons (CFCs) are photolytically cleaved in the stratosphere, releasing Cl• radicals. Each Cl• can destroy thousands of O₃ molecules catalytically.
SN2 proceeds in a single step with backside attack and inversion of configuration, while SN1 forms a planar carbocation intermediate first, leading to racemisation.
Concept context
Study carbon-halogen compounds: how they are made, how they react via SN1/SN2 and elimination, their stereochemistry, and their environmental impact.