See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Acidity Comparison of Phenolic Compounds **Key Principle:** Acidity of phenols depends on the stability of the conjugate base (phenoxide ion). Electron-withdrawing groups stabilize the negative charge on oxygen, increasing acidity. **Analysis of each compound:** **(1) 2-Nitrophenol:** $NO_2$ is a strong electron-withdrawing group (EWG). It pulls electron density away from the oxygen through resonance and inductive effects, stabilizing the phenoxide ion. **Most acidic.** **(2) 2-Methylphenol (o-cresol):** $CH_3$ is an electron-donating group (EDG). It destabilizes the phenoxide ion by increasing negative charge density on oxygen. **Less acidic than (1).** **(3) Phenol:** Unsubstituted benzene ring. No electron-withdrawing or donating effects. **Moderately acidic.** **(4) Chloroethanol:** An aliphatic alcohol, not a phenol. Aliphatic alcohols are much weaker acids than phenols. **Least acidic.** **Acidity Order:** $(1) > (3) > (2) > (4)$ **Answer: Option (1)** — 2-Nitrophenol is most acidic because the nitro group (strong EWG) stabilizes the resulting phenoxide ion through resonance delocalization and electron withdrawal, dramatically lowering the $pK_a$.