HCFCs are Class ___ ODS's and CFCs are Class ____ ODS's.

• A. I; II
• B. II; I
• C. II; II
• D. I; I

Answer: (B)

Ozone-depleting substances are grouped by how strongly they harm the ozone layer and how long they stay in the atmosphere. Class I includes the most damaging substances with long lifetimes, such as CFCs and halons. Class II covers substances with lower ozone-depletion potential and shorter atmospheric lifetimes, like HCFCs, which were developed as transitional substitutes. Because HCFCs have lower ozone-depleting potential and break down more before reaching the stratosphere, they fit into Class II, while CFCs, with higher potency and longer lifetimes, fit into Class I.