See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Determining Lowest $p K_a$ (Strongest Acid) **Key Principle:** Lower $p K_a$ = stronger acid. Electron-withdrawing groups (like Cl) adjacent to $-COOH$ stabilize the conjugate base ($-COO^-$), making the acid stronger. ## Analysis: **Option (1): $CH_3\text{-}CH(\text{Cl})\text{-}COOH}$** - Cl is one carbon away (β-position) - Weak inductive effect; moderate acid strength **Option (2): $Cl\text{-}CH_2\text{-}CH_2\text{-}COOH}$** - Cl is two carbons away (γ-position) - Very weak inductive effect; weakest acid in the series **Option (3): $CCl_3\text{-}COOH}$ ✓** - **Three Cl atoms directly attached to the carbon bearing $COOH$** - Strong cumulative inductive effect withdraws electron density - Dramatically stabilizes $-COO^-$ anion - Strongest acid; **lowest $p K_a$** **Option (4): $CHCl_2\text{-}COOH}$** - Two Cl atoms directly attached - Strong inductive effect, but less than (3) ## Answer: **(3) $CCl_3COOH$** The three electron-withdrawing chlorine atoms directly bonded to the carboxyl carbon maximally stabilize the conjugate base through inductive effects, making this the strongest acid with the lowest $p K_a$ value.