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 A

The question asks which statement about glucose is not true. Let's evaluate each option:

• Glucose is an aldose: Glucose is indeed an aldose, as it contains an aldehyde group at the first carbon. Hence, this statement is true.
• On heating with HI, glucose forms n-hexane: This is a characteristic reaction where the entire glucose molecule reduces to n-hexane when treated with hydrogen iodide. Thus, this statement is also true.
• It exists in furanose form: Glucose typically forms a pyranose ring when cyclized, not a furanose form. Therefore, this statement is not true about glucose.
• It does not give Schiff's test: Glucose does not give a positive Schiff's test because while it contains an aldehyde group, it forms a stable cyclic hemiacetal form that typically doesn't react with Schiff's reagent. Hence, this statement is true.

Considering the analysis above, the statement that is not true about glucose is: It exists in furanose form.

Answer 2

Step 1: Understanding glucose's properties. Glucose is an aldose (option A) and forms n-hexane on heating with HI (option B). It can exist in the furanose form (option C) as well.

 Step 2: Schiff's test. Glucose, being an aldehyde, will give a positive Schiff's test, which detects aldehydes. 

Step 3: Conclusion. Thus, the statement that glucose does not give Schiff's test is incorrect, corresponding to option (D).