Explain how the $-OH$ group attached to the carbon of the benzene ring activates the benzene ring for electrophilic substitution reactions.

(N/A) In phenol,the $-OH$ group is attached to the carbon of the benzene ring. The $-OH$ group acts as an activating group for electrophilic substitution reactions in the benzene ring.
The oxygen atom of the $-OH$ group possesses lone pairs of electrons. Through resonance,these lone pairs are delocalized into the benzene ring,as shown in the following resonance structures:
$(I)$ $\leftrightarrow$ $(II)$ $\leftrightarrow$ $(III)$ $\leftrightarrow$ $(IV)$ $\leftrightarrow$ $(V)$
These resonance structures clearly show that the electron density increases at the ortho and para positions of the ring due to the negative charge. As a result,the benzene ring becomes electron-rich,making it more susceptible to attack by electrophiles. Thus,the $-OH$ group activates the benzene ring for electrophilic substitution reactions.