Answer:
Cl2/FeCl3
Step-by-step explanation:
The electrophilic chlorination of aromatic compounds proceeds in the presence of Cl2/FeCl3.
The function of the Lewis acid FeCl3 is to 'activate' the chlorine molecule towards electrophilic substitution. This occurs by the formation of a 'chlorine cation' which attacks the aromatic ring followed by deprotonation of the aromatic ring to retain the aromaticity of the compound.