What is the function of $PCR$?

During $PCR$,denaturation of $DNA$ is achieved by which of the following?

After $4$ $PCR$ cycles,how many $DNA$ molecules are formed from one $DNA$ template molecule?

Refer to the following statements for agarose-gel electrophoresis:
$(a)$ The $\text{DNA}$ fragments resolve according to their size.
$(b)$ The separated $\text{DNA}$ fragment can be visualised only after staining with ethidium bromide followed by exposure to $UV$ radiation.
$(c)$ $\text{DNA}$ is always loaded into the well.
$(d)$ The smallest fragment of $\text{DNA}$ is near the well.
Choose the correct statements:

Which of the following diagrams is correct for primer annealing in $PCR$?

Significance of treating bacterial cells with calcium chloride before transformation is to facilitate