Question

what do you mean by charge is quantized

Answer 1

Charge is quantized because charge doesn't exists in the integral multiple.

Answer 2

Explanation:

Charge quantization, then, means that charge cannot take any arbitrary values, but only values that are integral multiples of the fundamental charge (charge of proton/electron). For example, in a hydrogen ion, we usually denote it with a positive sign to indicate that there's one proton more than there are electrons.