(N/A) The substitution of an $H$-atom of benzene by a $-Br$ group is known as bromination. In this reaction,$FeBr_3$ acts as a Lewis acid catalyst and $Br_2$ acts as the reagent.
$1$. Generation of Electrophile: The catalyst $FeBr_3$ reacts with $Br_2$ to generate the electrophile,bromonium ion $(Br^+)$.
$FeBr_3 + Br-Br \rightleftharpoons Br^+ + FeBr_4^-$
$2$. Mechanism: The reaction proceeds via electrophilic aromatic substitution in two steps:
Step $1$ (Slow step): The electrophile $Br^+$ attacks the benzene ring to form a carbocation intermediate known as a $\sigma$-complex or arenium ion. In this step,the carbon atom at the site of attack changes its hybridization from $sp^2$ to $sp^3$. This step is slow because the aromaticity of the benzene ring is temporarily lost.
The $\sigma$-complex is stabilized by resonance,as shown by structures $(A)$,$(B)$,and $(C)$,with $(D)$ representing the hybrid structure.
Step $2$ (Fast step): The $\sigma$-complex loses a proton $(H^+)$ to the $FeBr_4^-$ ion to restore aromaticity,forming bromobenzene and regenerating the catalyst $FeBr_3$ along with $HBr$.