See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Determining the Most Acidic Carboxylic Acid Carboxylic acid strength is determined by the stability of its conjugate base ($-COO^-$). More stable conjugates = stronger acids. ## Mechanism of Stability When $-COOH$ loses $H^+$, the resulting negative charge on oxygen is stabilized by: - **Electron-withdrawing groups** (EWG) near the carboxyl group pull electron density away, dispersing the negative charge - **Electron-donating groups** (EDG) destabilize the conjugate base ## Analysis of Each Option | Option | Group | Effect | Conjugate Base Stability | |--------|-------|--------|-------------------------| | **(A)** | $HO-$ | Electron-donating (mild) | Moderate | | **(B)** | $O_2N-$ | Highly electron-withdrawing | **Most stable** ✓ | | **(C)** | $Cl-$ | Electron-withdrawing (weak) | Good | | **(D)** | $NC-$ | Electron-withdrawing | Good | ## Why Option B is Strongest The **nitro group** ($O_2N-$) is the most powerful electron-withdrawing group due to: - Resonance stabilization through its two $N=O$ bonds - Inductive withdrawal of electrons - Greater effect than $Cl$ (halogen) or $CN$ (nitrile) The $O_2N-$ group maximally stabilizes the $-COO^-$ conjugate base, making the carboxylic acid most willing to donate its proton. **Answer: (B) $O_2N-CH_2-COOH$**