How many polynucleotide chains are present in the structure of $DNA$?

Which sugar is found in $RNA$?

Identify the nitrogenous bases of the purine and pyrimidine types.

If a $DNA$ molecule contains $10,000$ base pairs, how many nucleotides does it have?

$DNA$ exists in a double-stranded form whereas $RNA$ is mainly a single-stranded molecule. What is the likely reason for $DNA$ being double-stranded?

The base pairs of $DNA$ are correctly shown as