Which of the following is a purine?

The bond between the phosphate and sugar in a nucleotide is........

If a nucleic acid contains deoxyribose in its structure,it is called $DNA$ or $RNA$?

Select the correct option for a nucleoside.

Nucleic acids exhibit secondary structure. Justify with an example.

$P$: Nitrogen is essential for the synthesis of nucleic acids.
$Q$: Phosphorus is important in the structure of nucleic acids.