Biomolecules

The enzyme responsible for the hydrolysis of lactose into its constituent sugars, glucose and galactose, is β-galactosidase. This enzyme breaks the β-glycosidic bond between glucose and galactose in lactose, allowing their release as separate monosaccharides.
Options A (Transacetylase), B (Amylase), and C (Permease) are not associated with the hydrolysis of lactose.

So, the correct option is (D): β-galactosidase.