See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Acid Strength Analysis **Key Principle:** Acid strength depends on the stability of the conjugate base after proton loss. Electron-withdrawing groups (EWGs) stabilize the negative charge on the conjugate base, making the compound more acidic. ## Analysis of Each Option: **(A) Cyano + two $NO_2$ groups:** - $CN$ and $NO_2$ are EWGs, but the acidic proton is on the $CN$ group - Moderate electron withdrawal effect **(B) Three $NO_2$ groups:** - Three powerful EWGs on the benzene ring - However, the acidic proton is from $OH$ on the aromatic ring - Phenolic acidity (moderate strength) **(C) Two $NO_2$ + $COOH$:** - Two $NO_2$ groups are strong EWGs **on the benzene ring** - Acidic proton comes from the $COOH$ group (carboxylic acid is inherently strong) - The $NO_2$ groups **ortho and meta** to $COOH$ powerfully withdraw electrons through resonance and inductive effects - This stabilizes the conjugate base $COO^-$ maximally **(D) Two $NO_2$ + $CHO$:** - Aldehyde is less acidic than carboxylic acid - Weaker overall ## Conclusion: **Option (C) is strongest** because it combines: 1. An inherently strong carboxylic acid group ($pK_a \approx 3-4$ for aromatic carboxylic acids) 2. Two electron-withdrawing $NO_2$ groups positioned to maximize stabilization of the conjugate base