Which of the following organic functional group tests produces a silver mirror on the inner glass wall of a test tube upon reaction with aldehydes?
Answer and explanation
Correct answer: B. Tollens' reagent (ammoniacal silver nitrate)
- Step 1: Tollens' test uses a solution of silver nitrate in aqueous ammonia, containing [Ag(NH3)2]^+.
- Step 2: Aldehydes are oxidized to carboxylic acids while reducing silver ions to metallic silver (Ag^0), forming a characteristic reflective silver mirror.
- Step 3: Ketones do not react under standard Tollens conditions.
- Step 4: Identify Tollens' reagent.
Answer
Tollens' reagent (ammoniacal silver nitrate).
Why not the others: 'Fehling's solution' forms a brick-red precipitate of copper(I) oxide (Cu2O); 'Lucas reagent' (ZnCl2/HCl) tests for primary, secondary, and tertiary alcohols; 'Bromine water' tests for alkene unsaturation.
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