(A) The structure of disaccharide is shown below.

IIT-JEE 2005 Mains Chemistry - Biomolecules Question 6 English Explanation 1

The given disaccharide consists of two rings, first ring is acetal whereas second is hemiacetal. Due to presence of hemiacetal ring, the Tollen’s reagent will be able to react with this disaccharide. This is a reducing sugar.

(B) The structure of disaccharide is shown below.

IIT-JEE 2005 Mains Chemistry - Biomolecules Question 6 English Explanation 2

The given disaccharide is made up of two rings, both are acetal rings. Thus, this disaccharide is unable to react with Tollen’s reagent. This is a non-reducing sugar.

Final Answer :

(A) The disaccharide will reduce Tollen’s reagent.

(B) The disaccharide will not reduce Tollen’s reagent.

Hints :

The Tollen’s reagent is silver ammoniacal solution and is basic in nature. The Tollen’s reagent is used for distinguishing reducing and non-reducing sugars. The hemiacetal reacts with Tollen’s reagent, but acetal does not react with Tollen’s reagent.

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