In $DNA$,how are the nucleotides linked together?

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:

The genetic material in the bacterium $Escherichia$ $coli$ $(E. coli)$ is:

Purines of $DNA$ are represented by

If the $DNA$ of $E. coli$ is $1.36 \ mm$ long,how many base pairs $(bp)$ does it contain?

If a chromosome contains $2,00,000$ base pairs,how many nucleosomes will it have (in $,000$)?