Identify what is being asked

The question asks: among the isomeric forms (tautomers) of uracil, which form is present in RNA?

Recall the important concept

Uracil is a pyrimidine base present in RNA. Like many carbonyl-containing nitrogen heterocycles, it can exist in tautomeric forms:

• Lactam (keto) form
• Lactim (enol) form

In nucleic acids, the biologically relevant and predominant form is the lactam (diketo) form.

Structure of uracil in RNA

Uracil in RNA is specifically: $2,4\text{-dioxo pyrimidine}$ i.e. it contains two carbonyl groups at positions 2 and 4.

So the correct isomeric form must be the one showing:

• carbonyl group at $C_2$
• carbonyl group at $C_4$
• hydrogens on the two ring nitrogens as appropriate for the standard keto form

Choose the matching option

Since the standard form of uracil in RNA is the diketo (lactam) form, the correct option is the one corresponding to that structure.

From the stored answer, this is Option D.

Conclusion

The form of uracil present in RNA is the diketo (lactam) form.

Therefore, the correct answer is: $\boxed{D}$