Reducing sugars among the following are:
(A) Maltose
(B) Sucrose
(C) Lactose
(D) Fructose
(E) Cellulose
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, C and D only
Reducing sugars reduce Fehling’s solution and Tollens’ reagent. A sugar is reducing when it has a free aldehyde or ketone group (a free anomeric carbon). All monosaccharides, aldoses and ketoses alike, are reducing. In a disaccharide the sugar is reducing only if the glycosidic bond leaves one of these groups free.
(A) Maltose — Correct. Two α-D-glucose units are joined C1 to C4; the C1 of the second unit is free.
(B) Sucrose — Incorrect. The bond joins C1 of glucose to C2 of fructose, so both reducing groups are used up: sucrose is a non-reducing sugar.
(C) Lactose — Correct. β-D-galactose is joined C1 to C4 of β-D-glucose; C1 of the glucose unit is free.
(D) Fructose — Correct. It is a monosaccharide (a ketohexose); all monosaccharides are reducing sugars.
(E) Cellulose — Incorrect. It is a polysaccharide of thousands of β-D-glucose units; the reducing ends are negligible, so it does not reduce Fehling’s or Tollens’ reagent.
NCERT (2026-27 edition):
Classification of Carbohydrates – “… All those carbohydrates which reduce Fehling’s solution and Tollens’ reagent are referred to as reducing sugars. All monosaccharides whether aldose or ketose are reducing sugars.”
Disaccharides – “… In disaccharides, if the reducing groups of monosaccharides i.e., aldehydic or ketonic groups are bonded, these are non-reducing sugars, e.g., sucrose. On the other hand, sugars in which these functional groups are free, are called reducing sugars, for example, maltose and lactose.”