Lactose is a disaccharide formed from \(\beta \)-D-galactose and \(\beta \)-D-glucose. Identify anomeric carbon atoms in monosaccharide units

‘a’ carbon of galactose and ‘a’ carbon of glucose

The correct answer is option 3. ‘a’ carbon of galactose and ‘a’ carbon of glucose.

In the context of monosaccharides and disaccharides, the term "anomeric carbon" refers to the carbon atom that becomes asymmetric during the process of ring closure. In a cyclic structure, this carbon is known as the anomeric carbon, and it is labeled as either the α or β anomeric carbon.
For both \(\beta\)-D-galactose and \(\beta\)-D-glucose, the linkage in lactose involves the anomeric carbon of one monosaccharide reacting with a hydroxyl group on the other monosaccharide, forming a glycosidic bond.
In lactose, \(\beta\)-D-galactose is linked to \(\beta\)-D-glucose. This means that both monosaccharide units are in the \(\beta\) configuration. The anomeric carbon in \(\beta\)-D-galactose is the '1' carbon, and in \(\beta\)-D-glucose, it is also the '1' carbon.
Therefore, the correct answer is: (3) ‘a’ carbon of galactose and ‘a’ carbon of glucose