Question

Assertion (A) : p-nitrophenol is more acidic than phenol. Reason (R) : Nitro group is an electron-withdrawing group, it stabilises phenoxide ion by dispersal of negative charge.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Electron-withdrawing groups such as \[ -NO_2,\; -CN,\; -CHO,\; -COOH \] increase the acidity of phenols by stabilising the phenoxide ion. Electron-donating groups such as \[ -CH_3,\; -OCH_3,\; -NH_2 \] decrease acidity by destabilising the conjugate base.

Answer 1

The Correct Option is A

Step 1: Recall what determines phenol acidity.
Phenol's acidity depends on the stability of its conjugate base, the phenoxide ion ($C_6H_5O^-$). Any substituent that stabilises this anion increases acidity; electron-withdrawing groups do exactly this by dispersing the negative charge.
Step 2: Effect of the nitro group at the para position.
The $-NO_2$ group exerts strong electron-withdrawing effects ($-I$ and $-M$). At the para position it delocalises the negative charge on the phenoxide ion through the ring, making the conjugate base much more stable. Therefore p-nitrophenol releases a proton more readily than phenol: the Assertion is true.
Step 3: Evaluate the Reason and its explanatory power.
The Reason states that the nitro group is electron-withdrawing and stabilises phenoxide by dispersal of negative charge. This is exactly the mechanism responsible for the increased acidity. Both statements are true and the Reason correctly explains the Assertion.
\[ \boxed{\text{Option (A)}} \]