Identify what happens on boiling with dilute $H_2SO_4$ in alcoholic solution

Acid hydrolysis of a disaccharide gives its constituent monosaccharides.

Use the clue about products $A$ and $B$

We are told that two isomers $A$ and $B$ are formed.

• $A$ on oxidation with $HNO_3$ gives saccharic acid.
• Saccharic acid is obtained by oxidation of glucose.

Therefore, $A = \text{glucose}$

• $B$ is laevorotatory.
• The common monosaccharide formed in hydrolysis of sucrose along with glucose is fructose, which is laevorotatory.

Therefore, $B = \text{fructose}$

Now identify sugar $X$

The sugar that on hydrolysis gives glucose + fructose is sucrose.

$\text{sucrose} \xrightarrow[\text{alcoholic solution}]{\text{dil. }H_2SO_4} \text{glucose} + \text{fructose}$

Check the options

• A: Maltose $\to$ gives two units of glucose, not glucose + fructose.
• B: Sucrose $\to$ gives glucose and fructose. Correct.
• C: Lactose $\to$ gives glucose and galactose.
• D: Starch $\to$ gives glucose units only on hydrolysis.

Conclusion

Hence, $X = \text{sucrose}$