Which of the following bases is found only in $RNA$ but not in $DNA$?

Assertion $(A)$: Adenine and guanine are present in $RNA$ as purine bases.
Reason $(R)$: The base uracil is present in $RNA$.
The correct option among the following is:

The number of hydrogen bonds between guanine and cytosine; and between adenine and thymine in $DNA$ is

$RNA$ and $DNA$ are chiral molecules, their chirality is due to

The sugar units present in natural $DNA$ and $RNA,$ respectively are

The difference between $DNA$ and $RNA$ is based on the presence or absence of a hydroxyl group at which carbon atom of the sugar molecule?