Sugars can be reducing or nonreducing. Reducing sugars are those sugars that have free aldose or ketose group. Thus all monosaccharides are reducing sugars. Disaccharides like maltose and lactose are also reducing sugars. However sucrose is non reducing sugar. The glycosidic bond in sucrose is 1,2-glycosidic bond which means the bond is formed between the first carbon of glucose and second carbon of fructose. These carbons contain the functional groups too. Thus sucrose does not show any free functional group and hence it is a reducing sugar. Reducing sugars can be identified by Fehling's or Benedict's test.