Which of the following reagents would successfully distinguish between a reducing sugar and a non-reducing sugar?

Solution

1. Reducing sugars contain a free hemiacetal or hemiketal group that can open to an aldehyde or ketone.
2. $\text{Benedict’s reagent}$ contains ${\text{Cu}}^{2+}$ ions in an alkaline citrate solution.
3. The ${\text{Cu}}^{2+}$ is reduced to ${\text{Cu}}_2\text{O}$ (red precipitate) by the sugar.
4. Non-reducing sugars like sucrose do not react because their anomeric carbons are involved in a glycosidic bond.
5. Hence the answer is (A).