Which simple sugar is not classified as a reducing sugar?

The correct answer is sucrose, which is not classified as a reducing sugar. Reducing sugars are defined as sugars that have a free aldehyde or ketone group and can reduce other substances. They typically include monosaccharides and some disaccharides that contain a free anomeric carbon.

Sucrose, which is a disaccharide made up of glucose and fructose, does not have a free anomeric carbon when in its glycosidic bond. This lack of a free aldehyde or ketone group means that sucrose cannot act as a reducing agent. When sucrose is hydrolyzed into its constituent monosaccharides, both glucose and fructose can be classified as reducing sugars since they each have a free aldehyde functional group.

In contrast, monosaccharides like glucose and fructose, as well as disaccharides like lactose (which contains a free anomeric carbon), are capable of acting as reducing sugars because they can equate to the reducing form. This is significant in various biochemical contexts, including their reactions with certain reagents that test for reducing properties. Therefore, understanding the structure of sugars is key in determining their reducing capability, which is why sucrose stands out as the non-reducing sugar among