See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Acidity Comparison of Carboxylic Acids **Key Principle:** Acidity of carboxylic acids depends on the stability of their conjugate base (carboxylate anion). More stable anions = stronger acids. **Analysis by Structure:** 1. **Methoxy acetic acid** ($CH_3O-CH_2-COOH$): The methoxy group ($-OCH_3$) is electron-donating, destabilizing the negative charge on $COO^-$ → **weakest acid** 2. **Acetic acid** ($CH_3COOH$): Reference acid with no electron-withdrawing or donating substituents → **moderate acidity** 3. **Chloro acetic acid** ($Cl-CH_2-COOH$): Chlorine is weakly electronegative, withdraws electron density, stabilizing $COO^-$ → **stronger acid than acetic acid** 4. **Trifluoro acetic acid** ($CF_3COOH$): Three highly electronegative fluorine atoms strongly withdraw electrons through the $-CF_3$ group, maximally stabilizing the conjugate base → **strongest acid** **Ranking:** $CF_3COOH > ClCH_2COOH > CH_3COOH > CH_3OCH_2COOH$ **Answer: (4) Trifluoroacetic acid** is most acidic due to the extreme electron-withdrawing effect of the three fluorine atoms, which stabilizes the conjugate base most effectively.