Question

Which of the following statements is not true about glucose?

• A. It is an aldose.
• B. On heating with HI it forms n-hexane.
• C. It exists in furanose form.
• D. It does not give Schiff's test.

Hint:

Schiff's reagent tests for aldehydes, and glucose, being an aldose, will give a positive result.

Answer 1

The Correct Option is D

Let's analyze each statement:

A) It is an aldohexose:
This is true. Glucose is a six-carbon sugar (hexose) with an aldehyde functional group (aldo-).

B) On heating with HI it forms n-hexane:
This is also true. HI is a strong reducing agent that removes all oxygen atoms from glucose, reducing it to n-hexane.

C) It exists in furanose form:
This is partially true but misleading. While glucose can exist in both pyranose (six-membered ring) and furanose (five-membered ring) forms, the pyranose form is overwhelmingly predominant in solution. The furanose form exists only in minor amounts.

D) It does not give Schiff's test:
This is false. Glucose does give Schiff's test because its open-chain form contains an aldehyde group (in equilibrium with cyclic forms). Schiff's reagent reacts with aldehydes to produce a pink-magenta color.

Conclusion:
While statements A, B, and C have elements of truth, statement D is completely incorrect. The statement that is not true is (D).

Final Answer:
The incorrect statement is (D).