To identify the disaccharides A, B, and C, we need to understand the structure and components of common disaccharides.
Sucrose: Sucrose is a disaccharide composed of glucose and fructose. It is commonly known as table sugar. It is non-reducing because there is no free anomeric carbon.
Maltose: Maltose consists of two glucose units. These are connected by an α(1→4) glycosidic bond. It is a reducing sugar because one of the glucoses has a free anomeric carbon.
Lactose: Lactose is found in milk and is made up of one glucose and one galactose molecule. These are linked by a β(1→4) glycosidic bond. Lactose is also a reducing sugar due to the presence of a free anomeric carbon.
The correct order of disaccharides A, B, and C in the given correct answer is sucrose, maltose, lactose. This can be justified as follows:
The first disaccharide A is sucrose because it does not have a reducing end, which is a characteristic property distinguishing it from other disaccharides.
The second disaccharide B is maltose, identifiable by its two glucose units, where one has a free anomeric carbon, thereby making it a reducing sugar.
The third disaccharide C is lactose, that can be identified by its glucose and galactose combination with a β(1→4) glycosidic bond, also making it a reducing sugar.
Hence, the correct answer is sucrose, maltose, lactose.