Question

Assertion: Sucrose is a non-reducing sugar.
Reason: Sucrose is a disaccharide formed by glycosidic between $C - 1$ of $\alpha - gulcos e$ and $C - 2$ of $\beta - fructose$.
A) Both Assertion and Reason are correct and Reason is the correct explanation for assertion.
B) Both Assertion and reason are correct but reason is not the correct explanation for assertion.
C) Assertion is correct but Reason is incorrect
D) Both Assertion and Reason are incorrect.

Answer 1

Understand what is meant by disaccharide and non-reducing sugar for better answering this question. Disaccharides are formed from two monosaccharides and can be classified as either reducing or non-reducing. Non-reducing disaccharides like sucrose and trehalose have glycosidic bonds between their anomeric carbons and thus cannot convert to an open-chain form with an aldehyde group; they are stuck in the cyclic form.

Complete solution:
Let us begin by knowing about sucrose the answer will ultimately come out.
Sucrose is made up of two monosaccharides: glucose and fructose.
These two monosaccharides are held together by a glycosidic linkage between $C - 1$ of glucose and $C - 2$ of fructose.
Understand what is meant by glycosidic linkage: In sucrose, the monomers glucose and fructose are linked via an ether bond between $C - 1$ on the glucosyl subunit and $C - 2$ on the fructosyl unit. The bond is called a glycosidic linkage. Glucose exists predominantly as a mixture of $\alpha - glucose$ and $\beta - fructose$ "pyranose" isomers, but only the $C - 1$ form links to fructose.
Since the reducing groups of glucose and fructose (that is the free aldehyde/ketone groups) are involved in the glycosidic bond formation and are not available, sucrose is a non-reducing sugar.

Hence, both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

Note: Remember when sucrose is hydrolyzed it forms a 1:1 mixture of glucose and fructose. It is called invert sugar because the angle of the specific rotation of the plain polarized light changes from a positive to a negative value due to the presence of the optical isomers of the mixture of glucose and fructose sugar.