The statement that electric charge is an integral multiple of the electronic charge $e$ was experimentally proven by whom?

Select the correct alternative.

Two identical spherical conductors $B$ and $C$ have equal radii and carry equal charges. They repel each other with a force $F$ when placed at a certain distance apart. $A$ third identical spherical conductor $A$,which is uncharged,is brought in contact with $B$ and then removed. It is then brought in contact with $C$ and removed. What is the new force of repulsion between $B$ and $C$?

How much positive and negative charge is there in a cup of water $(250 \; g)$?

In a Millikan's oil drop experiment,the charge on an oil drop is calculated to be $6.35 \times 10^{-19} \ C$. The number of excess electrons on the drop is:

Why is a spark seen when removing synthetic clothes in the dark during winter?