Which one of the following correctly represents the manner of replication of $DNA$?

On which template strand of $DNA$ does continuous replication occur?

If a normal $DNA$ molecule replicates in an $N^{15}$ medium for consecutive generations,what is the percentage of light $DNA$ in the $4^{th}$ generation (in $\%$)?

An $E. coli$ cell with light $DNA$ is incubated in a culture medium containing a heavy isotope of nitrogen $(^{15}N)$. After $60$ minutes, find out the percentage of light $DNA$. (in $\%$)

If $E. coli$ is allowed to grow for $40$ minutes in a medium containing $^{15}N$,then the number of $^{14}N / ^{14}N$ containing $DNA$ molecules would be:

$DNA$ polymerase enzyme is responsible for the synthesis of