Lactose is disaccharide of

• A

  $\alpha$-D -glucose and $\alpha-D$-fructose
• Correct answer
  B

  $\beta-D$-glucose and $\beta$-D -galactose
• C

  $\alpha-D$-glucose and $\beta-D$-ribose
• D

  $\alpha-D$-glucose and $\beta-D$-galactose

Solution

Lactose is a disaccharide of $\beta-\mathrm{D}(+)$-glucose and $\beta-D(+)$-galactose. These monosaccharides are joined together with $\beta-1,4$-glycosidic linkage. It is a reducing sugar.

Hence, the correct answer is option: 'B'.