How many polynucleotide strands are present in the structure of $RNA$ and $DNA$ respectively?

Where is a cistron present?

In a hairpin model of $RNA$,which nitrogenous base is typically found at the loop end?

In a $DNA$ molecule,if the base ratio $(A+T)/(G+C)$ is $0.3$ and the amount of $A+T$ nitrogenous bases is $30,000$,what will be the amount of $G+C$ nitrogenous bases in the $DNA$ (in $,000$)?

What structure is formed when two polynucleotide chains in $DNA$ are coiled together?

Assertion: In a $DNA$ molecule,$A-T$ rich parts melt before $G-C$ rich parts.
Reason: In between $A$ and $T$ there are three $H-$ bonds,whereas in between $G$ and $C$ there are two $H-$ bonds.