See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: Reactivity in nucleophilic addition to carbonyl compounds depends on the electrophilicity of the carbonyl carbon. Greater the positive charge (or partial positive charge) on the carbonyl carbon, greater the reactivity. Electron-withdrawing groups (EWGs) increase reactivity; electron-donating groups (EDGs) decrease reactivity. Also, aldehydes are more reactive than ketones due to less steric hindrance and less electron donation by alkyl groups. Step 2 - Analyze each compound: (ii) 4-Nitrobenzaldehyde: CHO (aldehyde) + para-NO2 (strong EWG by resonance and induction). The NO2 group withdraws electron density from the ring and further from the carbonyl carbon, making it the most electrophilic. Highest reactivity. (i) Benzaldehyde: CHO (aldehyde) with no substituent on ring. Moderate reactivity as a baseline aromatic aldehyde. (iv) 4-Methylbenzaldehyde: CHO (aldehyde) + para-CH3 (EDG by hyperconjugation/induction). The methyl group donates electrons, slightly decreasing the electrophilicity of the carbonyl carbon compared to benzaldehyde. Lower reactivity than (i). (iii) Acetophenone: COCH3 (ketone). Two reasons for lower reactivity: (a) the methyl group is electron-donating relative to H, reducing electrophilicity; (b) greater steric hindrance at the carbonyl carbon compared to aldehydes. Lowest reactivity among these four. Step 3 - Order: ii > i > iv > iii Step 4 - Why other options fail: (a) ii > iii > i > iv: Incorrect because acetophenone (ketone) should be less reactive than benzaldehyde (aldehyde), not more; also iv should be less reactive than i, not the other way around as placed here. (c) iii > ii > i > iv: Incorrect because a ketone cannot be more reactive than an aldehyde with an EWG substituent. (d) iii > i > iv > ii: Incorrect for the same reason; ketone cannot be most reactive. Therefore, the correct answer is B.