Which is not correct?

glucose is a reducing sugar
glucose has six carbon atoms
glucose undergoes mutarotation
glucose is a disaccharide
glucose is an aldose

Most disaccharides are reducing sugars but glucose is a notable exception according to this web site.

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The statement "glucose is a disaccharide" is not correct.

To determine this, we need to understand the definitions and characteristics of the given statements.

1. Glucose is a reducing sugar: A reducing sugar is a sugar that can donate electrons to other molecules. Glucose is indeed a reducing sugar because it has a free aldehyde (reducing) group that can undergo oxidation-reduction reactions.

2. Glucose has six carbon atoms: Glucose is a monosaccharide, specifically a hexose, which means it has six carbon atoms. This statement is correct, as glucose does have six carbon atoms.

3. Glucose undergoes mutarotation: Mutarotation is the spontaneous interconversion between different anomeric forms (alpha and beta) of a sugar in aqueous solution. This statement is correct because glucose undergoes mutarotation, transitioning between its alpha and beta anomers.

4. Glucose is a disaccharide: This statement is not correct. A disaccharide is a sugar composed of two monosaccharide units joined together by a glycosidic bond. Glucose, on the other hand, is a monosaccharide, as mentioned earlier.

5. Glucose is an aldose: An aldose is a sugar that contains an aldehyde group (-CHO) as its most oxidized functional group. This statement is correct because glucose does have an aldehyde group, making it an aldose.

Therefore, the statement "glucose is a disaccharide" is the incorrect one out of the given options.