Which of the following is a disaccharide?

Lactose is indeed classified as a disaccharide because it is composed of two monosaccharide units: glucose and galactose. Disaccharides are carbohydrates formed when two monosaccharides undergo a dehydration synthesis reaction, resulting in a glycosidic bond. In the case of lactose, this bond connects the two sugar molecules, allowing it to serve as an important energy source, particularly in milk.

On the other hand, glucose and fructose are both monosaccharides, meaning they consist of only one sugar unit. Ribose is also a monosaccharide, specifically a pentose sugar, which has five carbon atoms and is significant in the structure of RNA. Recognizing these classifications is essential for understanding the structure and function of carbohydrates in biological systems.