Question

Compare acidic strength of the following compounds:
 (I) Phenol (II) \(p\)-Nitrophenol (III) \(p\)-Methylphenol (IV) \(p\)-Nitrobenzoic acid (V) Benzoic acid

• A. II \(>\) IV \(>\) V \(>\) I \(>\) III
• B. IV \(>\) V \(>\) III \(>\) I \(>\) II
• C. IV \(>\) V \(>\) II \(>\) I \(>\) III
• D. IV \(>\) II \(>\) I \(>\) V \(>\) III

Answer 1

The Correct Option is C

Concept: Acidic strength depends on the stability of the conjugate base. • Electron withdrawing groups increase acidity.
• Electron donating groups decrease acidity.
• Carboxylic acids are stronger acids than phenols.
Step 1: Compare carboxylic acids Carboxylic acids are stronger acids than phenols. Between them: \[ p\text{-Nitrobenzoic acid} > \text{Benzoic acid} \] because \(NO_2\) is a strong electron withdrawing group that stabilizes the conjugate base.
Step 2: Compare phenols Among phenols: \[ p\text{-Nitrophenol} > \text{Phenol} > p\text{-Methylphenol} \] Reason: • \(NO_2\) withdraws electrons \((-M,-I)\) increasing acidity.
• \(CH_3\) donates electrons \((+I)\) decreasing acidity.
Step 3: Combine the order \[ p\text{-Nitrobenzoic acid} > \text{Benzoic acid} > p\text{-Nitrophenol} > \text{Phenol} > p\text{-Methylphenol} \] Thus, [width=0.5]21c ans.png