Final answer:
Acetanilide will undergo bromination most rapidly using Br2, FeBr3 due to the electron-donating effect of its acetylamine group, which activates the benzene ring and increases its reactivity towards electrophiles.(Option c)
Step-by-step explanation:
Among these options, acetanilide will undergo bromination most rapidly. Acetanilide has an amino group (-NHCOCH3) which is an activating group for the benzene ring. This group is electron-donating through resonance, which increases the electron density on the ring and makes it more reactive towards electrophilic attack.
When comparing substituents on the aromatic ring, electron-donating groups like the acetylamine in acetanilide make the benzene ring more reactive to electrophiles like bromine, while electron-withdrawing groups and steric hindrance slow down the reaction. The other compounds either have electron-withdrawing groups, steric hindrance, or are already extensively substituted, which lessens their reaction speed under these conditions.