Carbohydrates

Comparing reducing and non-reducing disaccharides hinges on counting how many anomeric carbons remain free. Maltose is two glucose units joined by an alpha-1,4 glycosidic bond, and lactose is galactose linked to glucose by a beta-1,4 bond; in both cases only one of the two anomeric carbons is used in the linkage, leaving the other free. That free anomeric carbon can open into an aldehyde form, so it reduces Fehling's and Tollens' reagents and shows mutarotation, marking these as reducing sugars. In sucrose, the glucose C1 and fructose C2 anomeric carbons are both consumed by the glycosidic bond, leaving no free hemiacetal, so it is non-reducing. The claim about fructose is irrelevant because maltose and lactose contain no fructose. The alpha-versus-beta distinction does not determine reducing ability, since both alpha and beta linked sugars here are reducing. They are genuine disaccharides, not disguised monosaccharides. This follows the NCERT treatment of disaccharides. As a consistency check, the presence of exactly one free anomeric carbon predicts a single reducing end per molecule, which agrees with the observed positive tests.