Given $\mathrm{p}{K}_a$: benzoic acid 4.20, 4-nitrobenzoic acid 3.44, 3-nitrobenzoic acid 3.45, 2-nitrobenzoic acid 2.17. Which is the strongest acid, and why is it stronger than the para isomer?

1. A4-Nitrobenzoic acid; the nitro group exerts both $-M$ and $-I$ effects there
2. B3-Nitrobenzoic acid; only a $-I$ effect operates
3. C2-Nitrobenzoic acid; the ortho group adds the steric ortho effect to its electron-withdrawing effect
4. DBenzoic acid; it has no electron-withdrawing group