Question

Which of the following is most acidic? 

• A. A
• B. B
• C. C
• D. D

Answer 1

The Correct Option is B

Step 1: Acidic nature of substituents.
The acidity of substituted phenols depends on the electron-donating or electron-withdrawing effects of the substituent. Electron-withdrawing groups make the phenol more acidic, while electron-donating groups make it less acidic. Step 2: Analyzing the substituents.
- (A) \(\text{OCH_3\):} The methoxy group (\(\text{OCH}_3\)) is an electron-donating group, which makes the phenol less acidic by increasing the electron density on the oxygen, making it less likely to lose a proton.
- (B) \(\text{NO_2\):} The nitro group (\(\text{NO}_2\)) is a strong electron-withdrawing group, which decreases the electron density on the oxygen, increasing the acidity of the phenol.
- (C) \(\text{OH\) on benzene:} A simple phenol without any substituents other than the hydroxyl group is more acidic than a phenol with electron-donating groups, but less acidic than one with electron-withdrawing groups.
- (D) \(\text{CH_3\):} The methyl group (\(\text{CH}_3\)) is an electron-donating group, similar to the methoxy group, making the phenol less acidic.
Step 3: Conclusion.
The phenol with the nitro group (\(\text{NO}_2\)) attached is the most acidic, as it is the strongest electron-withdrawing group. (B) \(\text{OH}\) group attached to \(\text{NO}_2\) group.