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JEE Advanced levelSingle correct optionDifficulty 3 of 3si055

Aqueous solutions of glucose and fructose are to be distinguished. Which reagent works?

  1. ATollens reagent
  2. BMolisch reagent
  3. Cbromine water (buffered, mild)
  4. DBenedict's solution

Answer: C

Bromine water oxidises the aldehyde group of glucose to gluconic acid, but fructose, a ketose without a free CHO, is not oxidised. Tollens and Benedict's solution reduce both (fructose through enediol isomerisation in alkali), and the Molisch test is positive for all carbohydrates.
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