Explanation:

Monosaccharides are the simplest forms of sugar or simple sugars. They are the most fundamental unit of which all the carbohydrates are built. 

• Sucrose is not a monosaccharide, it is a disaccharide. Sucrose is formed of the monosaccharides fructose and glucose.

• Glucose is the simplest sugar or a monosaccharide and the preferred source of energy for the body. It is the main sugar found in the blood, it is the main source of energy, which one gets from the food.

• Fructose is a kind of sugar known as a monosaccharide. It is also called fruit sugar, as it is mainly found naturally in several fruits.

• Lactose: The sugar found naturally in milk, lactose is a disaccharide composed of one galactose molecule and one glucose molecule. Lactose is sometimes called “milk sugar.”

• Lactase is an enzyme which splits lactose into its component parts of glucose and galactose. Lactose is not an intensely sweet sugar; it is 70% less sweet than sucrose. However, its glucose and galactose are approximately twice as sweet as lactose.

• Galactose is monosaccharide sugar, which is about 65 percent as sweet as sucrose and as sweet as glucose. The molecule of galactose when associated with glucose forms a lactose molecule.

Hence option 2nd is correct.