Which of the following is incorrect for $DNA$ structure?

Assertion : In a $DNA$ molecule, $A-T$ rich parts melt before $G-C$ rich parts.

Reason : In between $A$ and $T$ there are three $H-$ bond, whereas in between $G$ and $C$ there are two $H-$ bonds.

If the distance between two consecutive base pairs is $0.34\, nm$ and the total number of base pairs of a $DNA$ double helix in a typical mammalian cell is $6.6 \times 10^{9}$ $bp,$ then the length of the $DNA$ is approximately 

Which amino acids are present in histones