Statement I: "Lactose is composed of α-D-glucose and β-D-glucose." Recall: Lactose (milk sugar) is a disaccharide consisting of β-D-galactose and β-D-glucose, linked by a β(1⟶4) glycosidic bond: β-D-Galactose - (1⟶4) - β-D-Glucose. Therefore, it is not composed of two glucose molecules - one of the units is galactose. Hence, Statement I is incorrect. Statement II: "Lactose is a reducing sugar." Explanation: In lactose, the glucose unit still has a free anomeric carbon (the hemiacetal group), so it can undergo mutarotation and reduce Benedict's or Fehling's solution. Thus, lactose is a reducing sugar. Statement II is correct.
