See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Acidity Order Analysis **Identify the compounds:** - **(I)** Phenol ($C_6H_5OH$) - **(II)** 4-Chlorophenol ($4-ClC_6H_4OH$) - **(III)** Benzoic acid ($C_6H_5COOH$) - **(IV)** 4-Methylbenzoic acid ($4-CH_3C_6H_4COOH$) --- **Key principle:** Acidity depends on: 1. **Type of functional group** — carboxylic acids ($-COOH$) are much stronger acids than phenols ($-OH$) 2. **Electronic effects** — electron-withdrawing groups increase acidity; electron-donating groups decrease acidity --- **Analysis by groups:** **Carboxylic acids (III > IV):** - $-CH_3$ is electron-donating (inductively), which destabilizes the conjugate base - $-COOH$ groups have $pK_a \approx 4$ - Therefore: **(III) > (IV)** **Phenols (II > I):** - $-Cl$ is electron-withdrawing, stabilizing the phenoxide ion ($C_6H_4O^-$) - $-Cl$ increases acidity of phenol - Phenols have $pK_a \approx 10$ - Therefore: **(II) > (I)** **Across groups:** - Carboxylic acids ($pK_a \approx 4$) are **much stronger** than phenols ($pK_a \approx 10$) - Therefore: **(III, IV) >> (II, I)** --- **Final order:** $$(III) > (IV) > (II) > (I)$$ **Answer: (A)**