In this reaction, the goal is to synthesize 1-methoxy-4-nitrobenzene, which involves replacing a halogen atom (bromine) with a methoxy group (\(-OCH_3\)) at the para position to the nitro group. This reaction typically proceeds through an S_N2 mechanism, where sodium methoxide (\(NaOCH_3\)) acts as a nucleophile and replaces the bromine atom. The methoxy group is a strong nucleophile and reacts efficiently with the electrophilic carbon bonded to the bromine in 1-bromo-4-nitrobenzene.
Thus, the most effective reaction is the one in option (A), where 1-bromo-4-nitrobenzene reacts with sodium methoxide to give 1-methoxy-4-nitrobenzene.
\[
\text{1-Bromo-4-nitrobenzene} + NaOCH_3 \rightarrow \text{1-Methoxy-4-nitrobenzene}
\]