What is the criterion for the movement of $DNA$ fragments on an agarose gel during gel electrophoresis?

Separated $DNA$ fragments on an agarose gel can be visualized after staining with ....

The technique used to make numerous copies of a specific segment of $DNA$ quickly and accurately is

Gel electrophoresis is used for

The blue and white selectable markers have been developed which differentiate recombinant colonies from non-recombinant colonies on the basis of their ability to produce colour in the presence of a chromogenic substrate.
Given below are two statements about this method :
Statement-$I$ : The blue coloured colonies have $\text{DNA}$ insert in the plasmid and they are identified as recombinant colonies.
Statement-$II$ : The colonies without blue colour have $\text{DNA}$ insert in the plasmid and are identified as recombinant colonies.
In the light of the above statements,choose the most appropriate answer from the options given below:

What is the first step in the Southern Blot technique?