Identify the nitrogenous base of nucleic acid from the following that has a double-ring structure.

In both $DNA$ and $RNA$,the heterocyclic base and phosphate ester linkage are present at which positions of the sugar respectively?

Which base is present in $RNA$ but not in $DNA$?

Which of the following nitrogen bases of nucleic acids is derived from purine?

Explain the structure of nucleic acids.

Uracil is a base present in $RNA$ with the following structure. The percentage of $N$ in uracil is $............$.
Given:
Molar mass $N = 14 \, g \, mol^{-1} ; O = 16 \, g \, mol^{-1} ; C = 12 \, g \, mol^{-1} ; H = 1 \, g \, mol^{-1}$.