Glucose
A sugar is only a reducing sugar if it has an open chain with an aldehyde or a ketone group. Monosaccharides which contain an aldehyde group are known as aldoses, and those with a ketone group are known as ketoses.
Reducing monosaccharides include glucose, fructose, glyceraldehyde and galactose. Many disaccharides, like lactose and maltose also do have a reducing form, as one of the two units may have an open-chain with an aldehyde group. However, sucrose and trehalose, in which the anomeric carbons of the two units are linked together, are non-reducing disaccharides.