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

$PCR$ is used for:

Which of the statements are correct about bioreactors?
$I.$ It provides all the optimal conditions for achieving the desired product by providing optimal growth conditions like temperature, $pH$, substrate, salt, vitamin and oxygen.
$II.$ It is suited for large-scale production of microorganisms under aseptic conditions for a number of days.

From the following tools/techniques of genetic engineering,identify those which are required for cloning a bacterial gene in animal cells and choose the correct option:
$I$. Endonuclease $II$. Ligase
$III$. $A. tumefaciens$ $IV$. Microinjection
$V$. Gene gun $VI$. Lysozyme
$VII$. Cellulase $VIII$. Electrophoresis

Ethidium bromide stained agarose gel is exposed to $.......,$ to observe $\text{DNA}$ as bright orange coloured bands.

Rapid antigen test and $RT$-$PCR$ are two diagnostic tests for the $COVID-19$ virus. $PCR$,a molecular diagnostic tool,stands for: