How many types of $DNA$ polymerases are present in bacteria?

Replication was allowed to take place in the presence of radioactive deoxynucleotide precursors in $E. coli$ that was a mutant for $DNA$ ligase. Newly synthesised radioactive $DNA$ was purified and strands were separated by denaturation. These were centrifuged using density gradient centrifugation. Which of the following would be a correct result?

$DNA$ polymerase enzyme is required for the synthesis of .......

During which process are Okazaki fragments formed?

Which property of $DNA$ double helix led Watson and Crick to hypothesise semiconservative mode of $DNA$ replication? Explain.

$E. coli$ bacteria grown in ${}^{15}NH_4Cl$ medium for several generations are allowed to grow in ${}^{14}NH_4Cl$ medium. After $2$ generations,the density gradient of the isolated $DNA$ is: