Which of the following is NOT considered a reducing sugar?

Sucrose is regarded as a non-reducing sugar because it does not have a free aldehyde or ketone group. In the context of carbohydrate chemistry, reducing sugars are those that can donate electrons or reduce another molecule, typically demonstrated by their ability to reduce agents like Benedict's or Fehling's solutions. In contrast, the structure of sucrose consists of a glucose and a fructose molecule linked together through a glycosidic bond, which locks the reactive functional groups in such a way that they are not available to participate in reduction reactions. Thus, while galactose, fructose, and glucose all contain free aldehyde or ketone groups, allowing them to act as reducing agents, sucrose’s unique structure prevents it from exhibiting such reducing properties.