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Carbohydrates are classified by the number of saccharide units and, for monosaccharides, by carbon number and whether they contain an aldehyde or ketone group. Their stereochemistry includes D/L forms, epimers, and α/β anomers; interconversion of anomers in solution produces mutarotation. Reducing sugars have a free hemiacetal and can be detected with several reagents, while sucrose and trehalose are non-reducing because their anomeric groups are involved in glycosidic linkages. Tests such as Molisch, Seliwanoff, and Bial’s help screen or distinguish carbohydrate types. Natural polysaccharides also have practical roles: starch is a storage material, cellulose is used in tablet formulations, and inulin is a marker for glomerular filtration rate.