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

The type of linkage present between nucleotides is

In a nucleoside,the base is attached to which position of the sugar molecule?

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

The reason for the double helical structure of $DNA$ is the operation of

The base adenine occurs in