What type of carbohydrate is formed by two monosaccharides joined together?

The type of carbohydrate that is formed by two monosaccharides joined together is known as a disaccharide. Disaccharides are the result of a condensation reaction, where a glycosidic bond forms between two monosaccharide units, resulting in the loss of a water molecule. Common examples of disaccharides include sucrose, which is made up of glucose and fructose, and lactose, which is made from glucose and galactose.

Oligosaccharides consist of a small number of monosaccharide units, typically between three to ten, which makes them longer than disaccharides. Polysaccharides are even larger, comprised of numerous monosaccharide units, usually more than ten, and they can form complex structures like starch, glycogen, or cellulose. Hexose refers specifically to monosaccharides that contain six carbon atoms, such as glucose and fructose, rather than describing their linkage or arrangement. Therefore, the clear identification of disaccharides as products of two monosaccharide units is what makes it the correct answer.