JEE Chemistry 2025 Question with Solution

Given: Statements about Ribose present in DNA are to be checked.

Find: Which listed statements are correct, and hence the correct option.

Check each statement one by one:

1. Statement A: Ribose is a pentose sugar. This is correct because ribose contains five carbon atoms.

2. Statement B: Ribose is present in pyranose form. This is incorrect because ribose generally exists in furanose form, not pyranose form.

3. Statement C: Ribose is in $\text{D}$ configuration. This is correct because biological ribose exists in the $\text{D}$-configuration.

4. Statement D: Ribose is a reducing sugar, when free. This is correct because in free form it can open to give an aldehyde group, so it behaves as a reducing sugar.

5. Statement E: Ribose is in $\alpha$-anomeric form. This is incorrect because ribose can exist in both $\alpha$ and $\beta$ forms; saying it is specifically in the $\alpha$ form is not generally correct.

Therefore, the correct statements are A, C and D only.

The correct option is A.

Given: The properties of Ribose are listed as statements A to E.

Find: Which combination of statements is true.

From the solution text:

• A. A pentose sugar — true.
• B. Present in pyranose form — false, because ribose is typically found in furanose form.
• C. In $\text{D}$ configuration — true.
• D. A reducing sugar, when free — true.
• E. In $\alpha$-anomeric form — false, because ribose may exist in both anomeric forms and is not characterized specifically by only the $\alpha$ form.

Hence the true set is A, C and D only, which corresponds to option A.