During $DNA$ replication,the strands separate by

Which bond does $DNA$ helicase break in $DNA$?

After the completion of replication,each $DNA$ molecule consists of:

In a nucleus,the number of ribonucleoside triphosphates is $10$ times the number of deoxyribonucleoside triphosphates,but only deoxyribonucleotides are added during $DNA$ replication. Suggest a mechanism.

New $DNA$ synthesis occurs in the $P$ direction,and the $DNA$ polymerase enzyme reads the template in the $Q$ direction.
$\quad \quad \quad \quad P \quad \quad \quad \quad \quad Q$

$A$ $DNA$ 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?