See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Tollens' reagent (ammoniacal silver nitrate) is a mild oxidizing agent that gives a positive silver mirror test with aldehydes (oxidized to carboxylates) but does NOT react with ketones, alcohols (secondary or primary non-aldehyde), or ethers. Step 1 - Evaluate each pair: (a) Benzaldehyde vs benzyl alcohol: Benzaldehyde is an aldehyde → positive Tollens' test (silver mirror). Benzyl alcohol is a primary alcohol but not an aldehyde → negative Tollens' test. These CAN be differentiated. (b) Hexanal vs 2-hexanone: Hexanal is an aldehyde → positive Tollens' test. 2-Hexanone is a ketone → negative Tollens' test. These CAN be differentiated. (c) 2-Hexanol vs 2-hexanone: 2-Hexanol is a secondary alcohol → negative Tollens' test. 2-Hexanone is a ketone → negative Tollens' test. BOTH give negative results with Tollens' reagent, so they CANNOT be differentiated by this reagent. (d) Pentanal vs diethyl ether: Pentanal is an aldehyde → positive Tollens' test. Diethyl ether is an ether → negative Tollens' test. These CAN be differentiated. Step 2 - Conclusion: The pair that cannot be differentiated by Tollens' reagent is 2-hexanol and 2-hexanone, because neither reacts with Tollens' reagent (no silver mirror formed with either compound). Therefore, the correct answer is C.