The pKa values of the conjugate acids are: $CH X_{3} OH$ 15.5, $C X_{6} H X_{5} OH$ 10.0, $p - O X_{2} N - C X_{6} H X_{4} - OH$ 7.15, $CH X_{3} COOH$ 4.76. For the four anions below, all attacking through oxygen with similar steric demand, nucleophilicity in a given solvent parallels basicity. The order of decreasing nucleophilicity is

A $CH X_{3} O X^{-} > p - O X_{2} N - C X_{6} H X_{4} - O X^{-} > C X_{6} H X_{5} O X^{-} > CH X_{3} COO X^{-}$
B $CH X_{3} O X^{-} > C X_{6} H X_{5} O X^{-} > p - O X_{2} N - C X_{6} H X_{4} - O X^{-} > CH X_{3} COO X^{-}$
C $C X_{6} H X_{5} O X^{-} > CH X_{3} O X^{-} > CH X_{3} COO X^{-} > p - O X_{2} N - C X_{6} H X_{4} - O X^{-}$
D $CH X_{3} COO X^{-} > p - O X_{2} N - C X_{6} H X_{4} - O X^{-} > C X_{6} H X_{5} O X^{-} > CH X_{3} O X^{-}$

Answer: B

Same attacking atom and similar size means nucleophilicity tracks basicity, i.e. the pKa of the conjugate acid. Ordering the pKa values 15.5 > 10.0 > 7.15 > 4.76 gives methoxide > phenoxide > 4-nitrophenoxide > acetate.

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Answer: B

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