Question

monosaccarides are called reducing sugars?but disaccharides are not.why?

Answer 1

Reducing sugars are the reducing groups ( aldehyde and ketonic group) are free and not bonded. These sugars are capable of reducing Fehling solution and Tollen's reagent.

Monosaccharides have free aldehydic or ketonic group, and are hence called reducing sugars.

Disaccharides do not have free aldehydic or ketonic groups but are bonded , and are hence called non reducing sugars.