See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Acid Strength Order ($K_a$ Values) ## Identify Each Compound: **(I)** $H_3N^⊕-CH_2-COOH$ → Zwitterionic amino acid (carboxyl group, electron-withdrawing $NH_3^+$) **(II)** $NC-CH_2-COOH$ → Nitrile substituent (strong electron-withdrawing via resonance) **(III)** $H_3C-CH_2-COOH$ → Propionic acid (alkyl substituent, weak electron-donating) **(IV)** $OOC^⊖-CH_2-COOH$ → Carboxylate anion (electron-donating, destabilizes conjugate base) ## Determine $K_a$ Order: **Strongest acid (I):** $NH_3^⊕$ group is highly electron-withdrawing (positive charge), stabilizes the conjugate base and activates the carboxyl group. **Second (II):** $CN$ group withdraws electrons through resonance, significantly stabilizing $COO^-$. **Third (III):** Alkyl group provides minimal electron withdrawal; behaves like typical carboxylic acid. **Weakest (IV):** Negatively charged $COO^⊖$ is electron-donating, destabilizes the second deprotonation and suppresses $K_a$. ## Result: $$K_a: \text{I} > \text{II} > \text{III} > \text{IV}$$ **Answer: (A)** ✓ Electron-withdrawing groups increase acidity by stabilizing the conjugate base; electron-donating groups decrease it.