Question Analysis: Assertion (A) and Reason (R) regarding Electrophilic Aromatic Substitution in Phenols.
Step 1 (Governing Principle): [0.5 Mark]
The $-\text{OH}$ group is a strongly activating group due to the +R (resonance) effect. The lone pair of electrons on the oxygen atom is delocalized into the benzene ring, increasing the electron density specifically at the ortho and para positions.
$$ \text{Resonance structures show high electron density at } o\text{- and } p\text{-positions.} $$Step 2 (Step-by-Step Logical Deduction): [0.25 Mark]
- Assertion (A): True. Because the $-\text{OH}$ group increases electron density at ortho and para positions via resonance, the incoming electrophile ($E^+$) is directed to these positions.
- Reason (R): True. The $+\text{R}$ effect of the $-\text{OH}$ group increases the overall electron density of the aromatic ring, thereby activating it towards electrophilic substitution.
- Correlation: The reason why the incoming group is directed to ortho and para positions is precisely because the ring is activated at those specific sites due to the resonance effect described in the reason. Thus, (R) is the correct explanation of (A).
Step 3 (Final Concluded Answer): [0.25 Mark]
Correct Option: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
💡 EL10 Concept Insight: Think of the $-\text{OH}$ group like a "faucet" that pours extra electrons into the benzene ring; because of how the ring is shaped, those extra electrons always pool up at the ortho and para spots, making those the perfect places for an incoming chemical to attach.