Which of the following is a disaccharide?

Sucrose is classified as a disaccharide because it is composed of two monosaccharide units: glucose and fructose. Disaccharides are sugars formed when two monosaccharides are linked together through a glycosidic bond, and sucrose is commonly found in many plants, serving as a primary form of energy storage. It is often referred to as table sugar and plays a significant role in nutrition due to its sweet flavor and energy-providing properties.

Other options listed have different classifications. Starch is a polysaccharide, which consists of many glucose units linked together, serving as a storage form of energy in plants. Cellulose, also a polysaccharide, is made up of a large number of glucose units, but its structure is more rigid, forming the cell walls of plants and providing structural support. Galactose is a monosaccharide; it is a single sugar unit that can combine with glucose to form lactose, another disaccharide, but on its own, it does not meet the criteria for being categorized as a disaccharide.