Identify the sugar in DNA

The sugar present in DNA is actually 2-deoxy-D-ribose, derived from ribose. The question asks about ribose, so let us evaluate the listed statements about ribose.

Check each statement

A. A pentose sugar

Ribose has 5 carbon atoms, so it is a pentose sugar.

Hence, A is correct.

B. Present in pyranose form

Ribose predominantly exists in furanose form in nucleic acids, not pyranose form.

Hence, B is incorrect.

C. In "D" configuration

Naturally occurring ribose is D-ribose.

Hence, C is correct.

D. A reducing sugar, when free

Free ribose has a hemiacetal/anomeric carbon that can open to the aldehyde form, so it behaves as a reducing sugar.

Hence, D is correct.

E. In $\alpha$-anomeric form

Ribose is not specifically always in the $\alpha$-anomeric form; both $\alpha$ and $\beta$ anomers can exist. In nucleic acids, the biologically relevant form is generally $\beta$.

Hence, E is incorrect.

Collect the correct statements

Correct statements are:

$A,\ C,\ D$

Match with the given options

• Option A: $A, D, E$ only — incorrect
• Option B: $B, D, E$ only — incorrect
• Option C: $A, C, D$ only — correct
• Option D: $A, B, E$ only — incorrect

Final answer

The correct option is:

$\boxed{\text{C}}$