Which of the following techniques is most commonly used to separate $DNA$ molecules by size?

Following enzymes/chemical/technique are used in the process of gel electrophoresis:
$I.$ sample $DNA$ is cut into fragments
$II.$ restriction endonucleases
$III.$ agarose gel
$IV.$ ethidium bromide
$V.$ $UV$-radiation
$VI.$ elution
Mark the correct sequence of their use.

Bioreactors are useful in

In gel electrophoresis,the separated $DNA$ fragments can be visualized by:

r-$DNA$ is inserted within the coding sequence of an enzyme,$\beta$-galactosidase. This results in the inactivation of the gene for the synthesis of this enzyme,which is referred to as . . . . . . .

$A$ simple stirred-tank bioreactor is shown below. Identify $A, B, C, D$,and $E$.