Which structure consists of two polynucleotide chains forming a helical structure?

In the double-helical structure of $DNA$,the two strands of $DNA$ are:

The nitrogenous bases of the two strands of $DNA$ are joined by

Given below are two statements:
Statement $I$: In prokaryotes,the positively charged $DNA$ is held with some negatively charged proteins in a region called nucleoid.
Statement $II$: In eukaryotes,the negatively charged $DNA$ is wrapped around the positively charged histone octamer to form nucleosome.
In the light of the above statements,choose the correct answer from the options given below:

In a $340 \text{ Å}$ long $DNA$ strand, how many nitrogen base pairs are present?

Select the correct option for $DNA$.