Typical question: Which of these compounds reacts faster with Br₂?

                               
Chlorobenzene                        Benzene

Right answer: Benzene.

It is common mistake to answer: Chlorobenzene.  The misunderstanding lies in the fact that many identify orto-para directors as activating agents.  In fact, many orto-para directors are activating agents.  However, halogens, while being orto-para directors, are deactivating agents.  Hence, Benzene will faster undergo electrophilic substitution.