Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Sucrose is a disaccharide and a non-reducing sugar.
Reason (R): Sucrose involves glycosidic linkage between $$C_1$$ of $$\beta$$-glucose and $$C_2$$ of $$\alpha$$-fructose.
Choose the most appropriate answer from the options given below:

We begin by recalling that a disaccharide is a carbohydrate that, on hydrolysis, yields two monosaccharide units. Sucrose, on hydrolysis, gives one molecule of glucose and one molecule of fructose, so sucrose is certainly a disaccharide.

Next, whether a sugar is reducing depends on the presence of a free anomeric carbon that can open up to give an aldehyde or ketone group capable of reducing Fehling’s or Tollen’s reagent. In sucrose, the anomeric carbon of glucose (its $$C_1$$) and the anomeric carbon of fructose (its $$C_2$$) are both tied up in the glycosidic bond. Because both potentially reducing centers are blocked, sucrose cannot convert into an open-chain form and hence cannot act as a reducing agent. Therefore, sucrose is classified as a non-reducing sugar.

So far, we have confirmed every part of the Assertion (A): “Sucrose is a disaccharide and a non-reducing sugar.” Both statements are correct.

Now we analyse the Reason (R). The accepted structural description of sucrose is

$$\alpha\text{-D-glucopyranosyl} \,(1 \rightarrow 2)\, \beta\text{-D-fructofuranoside}$$

This wording tells us explicitly that the glycosidic linkage joins

$$C_1$$ of $$\alpha$$-D-glucose to $$C_2$$ of $$\beta$$-D-fructose.

However, the Reason (R) claims that the linkage is between $$C_1$$ of $$\beta$$-glucose and $$C_2$$ of $$\alpha$$-fructose. Both the configuration of glucose and of fructose have been reversed in this statement, and thus the description is wrong.

Therefore, the Reason (R) is false even though the Assertion (A) is true. Because a false statement cannot be the correct explanation of a true statement, we conclude that the correct choice is the one where Assertion is true but Reason is false.

Hence, the correct answer is Option B.