Which base is present in $RNA$ instead of $Thymine$?

Which base is present in $RNA$ but absent in $DNA$?

In $DNA$,the base units are linked by which of the following?

$A$ nucleotide consists of

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

In $DNA$ and $RNA$,the heterocyclic base and phosphate ester are attached to which carbons of the sugar molecule,respectively?