At what time intervals did Meselson and Stahl take samples after transferring the bacteria to a $^{14}NH_{4}Cl$ medium?

Given below are two statements.
Statement $I$ - The template strand with free $3'$ end is called leading template and the strand with free $5'$ end is called lagging template.
Statement $II$ - Replication always starts at the $3'$ end of the template strand and proceeds towards the $5'$ end of the template.
In the light of the above statements,select the correct option given below:

Which of the following did Meselson and Stahl use in the experiment to prove semiconservative $DNA$ replication?

During in vitro synthesis of $DNA$,a researcher used $2', 3'$-dideoxy cytidine triphosphate as raw nucleotide in place of $2'$-deoxy cytidine. What would be the consequence?

In Meselson and Stahl's experiments,heavy $DNA$ was distinguished from normal $DNA$ by centrifugation in

Given below are the two statements.
Statement $I$: In prokaryotes,there is only one replicon,however,in eukaryotes,there are several replicons in tandem.
Statement $II$: The two separated strands in a replicon of $DNA$ are prevented from rejoining by helicase enzyme.
In the light of the above statements,choose the correct answer from the options given below.