All the charges found in nature are integral multiples of a basic unit of charge denoted by

e. "This fact is called Quantisation".

Thus charge $q$ on a body is always given by

$q=n e$ where $n$ is positive or negative integer.

The quantisation of charge was first suggested by the experimental laws of electrolysis discovered by English experimentalist Faraday. It was experimentally demonstrated by Millikan in $1912 .$

The main reason of quantisation is that when two bodies are rubbed, only integer no. of electrons are transferred from one body to another.