Question

Why is glucose a 'reducing sugar'?

• A. it has a ketone group
• B. it contains an aldehyde group
• C. it is a monosaccharide
• D. glucose is not a reducing sugar

Answer 1

The correct option is B

it contains an aldehyde group

All monosaccharides are reducing sugars because all monosaccharides have an aldehyde group (if they are aldoses) or can tautomerize in solution to form an aldehyde group (if they are ketoses). This includes common monosaccharides like galactose, glucose, glyceraldehyde, fructose, ribose, and xylose. They are called 'reducing sugars' because the presence of the aldehyde group makes them undergo oxidation readily to form carboxylic acid and in the process the reactive reagents are reduced easily.