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

There are two metallic spheres of same radii,but one is solid and the other is hollow. Then:

When is a charge considered a point charge?

What is the total charge of the electrons in a neutral atom?

$A$ $1$ paisa coin is made up of an $Al-Mg$ alloy and weighs $0.75\, g$. It has a square shape and its diagonal measures $17\, mm$. It is electrically neutral and contains equal amounts of positive and negative charges. Calculate the total amount of positive or negative charge in the coin.

What are called electrically charged and electrically neutral bodies?