On what basis are $DNA$ fragments separated in agarose gel electrophoresis?

What is the ultimate objective of $r-DNA$ technology?

$A$ transformed bacterium with a human gene fails to produce the desired protein. The reason could be:

Study the given figure carefully and select the correct statements regarding this.
$I.$ It represents typical agarose gel electrophoresis showing differential migration of $DNA$ fragments.
$II.$ Lane $1$ contains undigested $DNA$ fragments.
$III.$ Lanes $2$ to $4$ contain digested $DNA$ fragments.
$IV.$ Smallest $DNA$ bands are present at $(A)$ position and largest $DNA$ bands are present at $(B)$ position.

In the $PCR$ technique,how are the two strands of $DNA$ separated?

Gene amplification using primers can be done by