What is quantization of charge? What is the reason for quantization?

(N/A) Quantization of charge is the property by virtue of which all free charges are integral multiples of a basic unit of charge, denoted by $e$. This means that any charge $q$ on a body can be expressed as $q = ne$, where $n$ is an integer $(n = 0, \pm 1, \pm 2, \dots)$ and $e \approx 1.602 \times 10^{-19} \ C$.
The quantization of charge was first suggested by the experimental laws of electrolysis discovered by the English scientist Michael Faraday. It was later experimentally demonstrated by Robert Millikan in $1912$.
The fundamental reason for quantization is that during the process of charging (such as rubbing two bodies together), only an integral number of electrons can be transferred from one body to another. Since an electron cannot be divided into smaller parts, the charge transferred must always be an integer multiple of the elementary charge $e$.