Question

The functional group(s) in reducing sugar that tests positive with Tollen’s reagent is (are)

• A. Aldehyde
• B. Ketone
• C. Hemi-acetal
• D. Acetal

Hint:

Only functional groups that can yield a free aldehyde in solution will give a positive Tollen’s test — typical of reducing sugars.

Answer 1

The Correct Option is A, B, C

Step 1: Recall what Tollen’s reagent detects.
Tollen’s reagent is an ammoniacal solution of silver nitrate that oxidizes aldehydes (–CHO) to carboxylates while reducing Ag$^+$ to metallic silver (silver mirror test).
Step 2: Relation to reducing sugars.
- Reducing sugars (like glucose) contain a free aldehyde or a hemiacetal group that can open up to form an aldehyde in solution.
- Ketones (like in fructose) do not directly react unless tautomerization produces an aldehyde form.
- Acetals are stable and do not react with Tollen’s reagent.
Step 3: Conclusion.
Reducing sugars test positive due to the presence of aldehyde or hemiacetal groups.