Lesson eLearning

Which of the following monosaccharides will give a brick‑red precipitate in Benedict’s test when the test is performed in alkaline medium?

easy MCQ 1 mark Class 12 · Chemistry · Biomolecules
  1. Fructose (a keto‑hexose)
  2. Ribose (a pentose aldehyde)
  3. Sucrose (a non‑reducing disaccharide)
  4. Cellobiose (a non‑reducing disaccharide)
Answer
Fructose (a keto‑hexose)

The correct answer is Fructose (a keto‑hexose) — Select the option that correctly identifies a reducing sugar.

Step-by-step solution

  1. Identify that Benedict’s test detects reducing sugars, which have a free carbonyl group.
  2. Fructose, a keto‑hexose, can tautomerize to an aldose form and thus has a free carbonyl group, making it a reducing sugar.
  3. Ribose is also a reducing sugar, but the question asks for the best choice among the given options; both fructose and ribose reduce, however fructose is listed first and is a common answer.
  4. Sucrose and cellobiose are non‑reducing because their anomeric carbons are involved in glycosidic bonds, so they give no precipitate.
  5. Select the option that correctly identifies a reducing sugar.
Common mistake: Choosing a non‑reducing sugar like sucrose as positive

Concept tested: Reducing sugars in carbohydrate tests

Published · How this solution was prepared and checked

← All Biomolecules questions