The data below are assumed for this problem: ODP (relative to CFC-11 = 1.00) and 100-year GWP (relative to $\mathrm{CO}{}_2$ = 1). Gas P: ODP 1.00, GWP 4700. Gas Q: ODP 0.05, GWP 1800. Gas R: ODP 0, GWP 1400. Gas S: ODP 0, GWP 1. Which interpretation is correct if P, Q, R, S are CFC-11, an HCFC, an HFC and $\mathrm{CO}{}_2$ respectively?

1. AP has no warming effect because its ODP is high
2. BR is chemically identical to S because both have ODP zero
3. CR harms ozone least among the halocarbons but still warms the climate much more than the same mass of $\mathrm{CO}{}_2$
4. DQ is the best replacement since its ODP is nonzero and GWP is lower than P