Which of the following is non reducing sugar?

Reducing sugars are carbohydrates that can act as reducing agents due to the presence of a free aldehyde or ketone group. All monosaccharides, such as fructose, are reducing sugars.

In disaccharides, if the reducing groups of the monosaccharides are involved in forming the glycosidic bond, the sugar is non-reducing. In sucrose, the glycosidic linkage is formed between the C1 (anomeric carbon)$of \alpha$-D-glucose and the C2 (anomeric carbon)$of \beta$-D-fructose. Since both reducing groups are involved in the bond formation, sucrose does not have a free aldehyde or ketone group.

In contrast, maltose and lactose have free hemiacetal groups at one of their anomeric carbons, making them reducing sugars.

Therefore, sucrose is a non-reducing sugar.

Answer: Sucrose