See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Acidity in Aromatic Compounds **Step 1: Identify the acidic functional groups** All compounds contain either $-OH$ or $-CO_2H$ groups. The $-CO_2H$ group is inherently more acidic than $-OH$ on benzene (phenol). This eliminates option (1). **Step 2: Compare carboxylic acids (options 2, 3, 4)** For $-CO_2H$ groups attached to benzene, acidity depends on the electron-donating/withdrawing nature of substituents on the ring. **Step 3: Apply the inductive effect** - **Option (2)**: Benzoic acid with no substituents — baseline acidity - **Option (3)**: Methyl group ($-CH_3$) is electron-donating (weakens acidity) - **Option (4)**: Nitro group ($-NO_2$) is strongly electron-withdrawing **Step 4: Effect of electron-withdrawing groups** The $-NO_2$ group withdraws electron density from the benzene ring through the inductive effect, which destabilizes the negative charge on the resulting carboxylate anion $-CO_2^-$ *less* effectively and makes deprotonation more favorable. This increases acidity. **Step 5: Resonance and stabilization** The nitro group's electron withdrawal stabilizes the conjugate base by reducing electron density on the aromatic ring, making loss of the proton more favorable. **Answer: Option (4)** is the most acidic because the electron-withdrawing $-NO_2$ group enhances the acidity of the adjacent carboxylic acid group through inductive effects.