Which bonds does helicase break in $DNA$?

During the polymerization of deoxyribonucleoside triphosphates in bacteria,which of the following enzymes is mainly required?

Which organism was used as experimental material to study $DNA$ replication?

Match List-$I$ with List-$II$ and select the correct answer using the code given below in the lists.

List-$I$	List-$II$
$a$. Ligase	Joins short segments of $\text{DNA}$ together.
$b$. $\text{DNA}$ polymerase	Cuts $\text{RNA}$ at specific $\text{RNA}$ sequence.
$c$. Helicase	Breaks the hydrogen bonds between complementary pairs during $\text{DNA}$ replication.

$A$ $DNA$ 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?

Escherichia coli is completely labeled with $N^{15}$ and then grown in an $N^{14}$ medium. What will be the nature of the two $DNA$ strands in the first generation of bacteria?