In an electrophilic substitution reaction, an electron deficient species attacks the benzene ring which is e$^{–}$ rich. 1When an –OH group is attached to the benzene ring, by the virtue of its electron releasing nature increases the e$^{–}$ density ofthe ring and thus activates it, i.e., makes it a welcome site for electrophiles. The increase in electron density can be visualised as :From structures (I) - (V), we find that the attachment of hydroxyl group to benzene has increased the electron density (–ve charge) on the ring carbon atoms (especially C-2, C-4 and C-6). It is therefore said to have activated the ring towards electrophiles which are attracted to the increased electron density.