What is the electrophilic reactant B in the following reaction scheme?

Question

Quizplus · Accepted Answer

The key to identifying the electrophilic reactant is to look for the species with an electron-deficient or partially positive atom that can act as a site of attack for a nucleophile. In this case, we see that the reactant labeled as B has a partially positive sulfur atom due to the electron-withdrawing effect of the nitro group. This makes B an electrophile that can react with the nucleophilic benzene ring to form a new bond. Out of the answer choices, only C has a nitro group attached to a sulfur atom, so C is the best choice for the electrophilic reactant.

What Is the Electrophilic Reactant B in the Following Reaction