Explain how does the `(---OH)` group attached to a carbon of benzene ring activate it towards electophililc substitution.

Explanation

Phenol may be regarded as a resonance hybrid of structures, As a result of +R-efffect of the OH group, the electron density in the benzene ring increases thereby facilitating the attacck by an electrophile. In other words, presence of OH group, activates the benzene ring towards electrophilic substitution reactions. further since the electron density is relatively higher at the two o- and one p- position, therefore, electrophilic substitution occurs mainly at o- and p-positions.