Which of the following enzymes plays a major role in the synthesis of a new $\text{DNA}$ strand during $\text{DNA}$ replication?

If $E. coli$ is grown in a $^{15}N$ medium for $80$ minutes,starting from a $^{14}N$ medium,what will be the ratio of light to hybrid $DNA$ molecules obtained?

Which enzyme catalyzes the process of reverse transcription?

Distinguish between: Leading strand and Lagging strand.

$A$ $DNA$ molecule in which both strands have radioactive thymidine is allowed to duplicate in an environment containing non-radioactive thymidine. What will be the correct number of $DNA$ molecules that contain some radioactive thymidine after three duplications?

$A$ $N^{15}-N^{15}$ $\text{DNA}$ molecule is continuously replicated in $N^{14}$ medium,then what is the percentage of heavy $\text{DNA}$ in the $4^{\text{th}}$ generation (in $\%$)?