Chemistry - GOC Question with Solution | TestHub

Ethanol (pKa about 16) is a weaker acid than ethanethiol (pKa about 10.6), which means the ethoxide ion (I) is the stronger base. In protic solvents, the small O^- is held tightly by hydrogen bonds. In contrast, the larger, more polarizable S^- is only weakly solvated, making its electrons more available. Therefore, II is the better nucleophile. Consequently, I is more basic but less nucleophilic than II. The correct answer is (B).