Oligosaccharides are carbohydrates yielding two to ten monosaccharide units upon hydrolysis. Disaccharides, a common type, produce two monosaccharide units, which may be the same or different. For instance, sucrose hydrolysis yields glucose and fructose, while maltose provides two glucose molecules.

A monosaccharide is a carbohydrate that cannot be further hydrolyzed and represents a polyhydroxy aldehyde or ketone unit. Examples include glucose, fructose, and ribose.

Chemically, carbohydrates are defined as optically active polyhydroxy aldehydes or ketones, or compounds that produce such units on hydrolysis. Sugars like sucrose and lactose, common carbohydrates, are also referred to as saccharides, deriving from the Greek word “sakcharon,” meaning sugar.

Acetic acid fits the general formula C₂(H₂O)₂ but is not a carbohydrate because carbohydrates are defined as optically active polyhydroxy aldehydes or ketones, and acetic acid lacks these specific functional groups.

The general formula for carbohydrates is Cₓ(H₂O)ᵧ. The term “carbohydrate” originates from the idea that these compounds are hydrates of carbon, as seen in the molecular formula of glucose (C₆H₁₂O₆).