Three structures are given below in which two glucose units are linked. Which of these linkages between glucose units are between C1 and C4 and which linkages are between C1 and C6.Is the compound (I) reducing in nature? Explain.

I and III have the C1 and C4 linkage between them whereas the II compound has a C1 and C6 linkage between them.

Yes compound I is a reducing sugar as C1 of glucose in solution is free and shows reducing properties.

Compound I is lactose.