Which of the glycosidic linkage between galactose and glucose is present in lactose?

Lactose is a disaccharide composed of one unit of D-galactose and one unit of D-glucose. It is commonly known as milk sugar.

In lactose, the glycosidic bond is formed between the anomeric carbon (C-1) of $$\beta$$-D-galactose and the C-4 hydroxyl group of D-glucose. This is a $$\beta$$-1,4-glycosidic linkage.

The galactose unit provides its C-1 carbon for the glycosidic bond, while the glucose unit provides its C-4 carbon. Since the anomeric carbon of glucose remains free and is not involved in the glycosidic bond, lactose is a reducing sugar.

Therefore, the glycosidic linkage in lactose is between C-1 of galactose and C-4 of glucose, which corresponds to Option 3.