[zeoblade]

In a section on halogenation of benzene, a question asks, "why does hydration inactivate FeBr3?"

Maybe I can't understand what they are asking. Are they asking to add water to benzene? Or hydrating FeBr3?

Water coordinating to Fe as a ligand will inactivate FeBr3 to catalyse halogenation of benzene?

[Schrödinger]

Well, I'm guessing that H2O, as you said binds to FeBr3, which is a Lewis acid, and prevents breakdown of the Br-Br bond.
    Br2 + FeBr3 = Br+ + [FeBr4]-
   The above reaction might not occur due to the absence of FeBr3

Please correct me if I'm wrong.