Explanation:
In maltose, free aldehyde group can be produced at \(\mathrm{C_{1}}\) of second glucose in solution and it shows reducing properties so it is a reducing sugar.
Lactose is composed of \(\mathrm{\beta}\)-D -galactose and \(\mathrm{\beta}\)-D -glucose. The linkage is between \(\mathrm{C_{1}}\) of galactose and \(\mathrm{C_{4}}\) of glucose. Hence, it is also a reducing sugar.