Which one of the following is a non-reducing carbohydrate? 
(b) Sucrose is a disaccharide of glucose and fructose. It is a non-reducing sugar as it do not contain any free anomeric carbon atom. Maltose is a disaccharide of 2 glucose units. Its first glucose residue cannot undergo oxidation, whereas, second residue can undergo oxidation because it has a reactive free anomeric carbon atom. Hence, it is a reducing sugar.
Lactose and Ribose-5-phosphate are also reducing in nature due to the presence of a free ketonic or aldehyde group.