See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: The acidity of substituted phenols depends on the ability of substituents to stabilize or destabilize the phenoxide anion formed after deprotonation. Electron-withdrawing groups (EWGs) stabilize the negative charge on the phenoxide and increase acidity; electron-donating groups (EDGs) destabilize it and decrease acidity. Step 2 - Analyze Compound 2 (2,4,6-trimethylphenol): Methyl groups are electron-donating via hyperconjugation and induction. Three methyl groups (at ortho and para positions) increase electron density on the ring and on oxygen, destabilizing the phenoxide anion. This makes compound 2 the weakest acid among the three. Step 3 - Analyze Compound 1 (2,4,6-trichlorophenol): Chlorine is weakly electron-withdrawing by induction (−I effect) but also has a +M (resonance donation) effect. The net effect of three Cl substituents is moderate electron withdrawal, moderately stabilizing the phenoxide. This makes compound 1 more acidic than compound 2 but less acidic than compound 3. Step 4 - Analyze Compound 3 (2,4,6-trinitrophenol, picric acid): Nitro groups are strongly electron-withdrawing by both induction and resonance (−I and −M). Three nitro groups at ortho and para positions very effectively delocalize and stabilize the negative charge on the phenoxide through resonance. This makes compound 3 (picric acid) the strongest acid of the three — it is a well-known strong acid among phenols (pKa ≈ 0.38). Step 5 - Order of increasing acidity (weakest first): Compound 2 (weakest) < Compound 1 < Compound 3 (strongest), i.e., 2 < 1 < 3. Step 6 - Why other options fail: - (a) 2 < 3 < 1: Wrong — places trichlorophenol as most acidic, but trinitrophenol is far more acidic. - (b) 3 < 1 < 2: Wrong — reverses the order entirely; trinitrophenol is the strongest acid, not weakest. - (c) 1 < 2 < 3: Wrong — places trimethylphenol as more acidic than trichlorophenol, but methyl groups are electron-donating and should decrease acidity. Therefore, the correct answer is D.