S

Shyam Dubey • 3.70K Points
Extraordinary

Q. Which reagent is commonly used to distinguish between aldehydes and ketones (Tollens' test)?

  • (A) Tollen's reagent (ammoniacal Ag+)
  • (B) 2,4-Dinitrophenylhydrazine (DNPH)
  • (C) Bromine water
  • (D) Fehling's solution
  • Correct Answer - Option(A)
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Explanation by: Shyam Dubey
Tollens' reagent (Ag(NH3)2+) oxidizes aldehydes to carboxylates and reduces Ag+ to metallic silver, producing a silver mirror — a positive test for aldehydes. DNPH reacts with both aldehydes and ketones to form hydrazones, so it doesn't distinguish them. Bromine water tests for unsaturation or phenols (and some active methylene compounds). Fehling's solution also distinguishes aldehydes (reducing) from many ketones, but Tollens' reagent is the classic answer here; Fehling's would also be acceptable in some contexts but not listed as the correct choice here.

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