The nitrogen base found only in $DNA$ is also called

$DNA$ segments that can switch their position are called:

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.

Select the option that represents the organisms in ascending order of their $DNA$ length.

Chargaff's rule is given as:

If a double-stranded $DNA$ has $30 \%$ adenine,what is the percentage of cytosine in the same $DNA$ (in $\%$)?