In $PCR$ technique,how many copies of the $DNA$ sample will be obtained after $6$ cycles are completed?

What treatment is given to make a bacterial cell competent to take up $DNA$?

During the process of isolation of $DNA$,chilled ethanol is added to

$I. ... A...$ is the ability of a cell to take up foreign $DNA$.
$II.$ The cell is treated with a specific concentration of a divalent cation such as $... B...$ to increase the pore size in the cell wall.
$III.$ In $...C...$ method,recombinant $DNA$ is directly injected into the nucleus of an animal cell.
The most appropriate option regarding $A, B$ and $C$ is:

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 . . . . . . .

Bioreactors are useful in