Chemistry - Biomolecules Question with Solution | TestHub

Reducing sugars are carbohydrates that have a free aldehyde or ketone group (hemiacetal or hemiketal form) capable of acting as a reducing agent.

Lactose is a disaccharide formed by $\beta$-D-galactose and $\beta$-D-glucose with a $\beta -1,4$-glycosidic linkage. The anomeric carbon of the glucose unit is free, making it a reducing sugar.

Fructose is a monosaccharide containing a ketose group, which can isomerize to an aldose in an alkaline medium, making it a reducing sugar.

Sucrose is a disaccharide formed by $\alpha$-D-glucose and $\beta$-D-fructose. The glycosidic linkage involves the anomeric carbon of glucose (C1) and the anomeric carbon of fructose (C2). Since both anomeric carbons are involved in the bond, there is no free hemiacetal or hemiketal group. Thus, sucrose is a non-reducing sugar.

Maltose is a disaccharide formed by two $\alpha$-D-glucose units with an $\alpha -1,4$-glycosidic linkage. The anomeric carbon of the second glucose unit is free, making it a reducing sugar.

Answer: Sucrose