What is the minimum charge on a particle?

The correct option is 1.6 x 10^-19 Coulomb.

Electric charge is a quantized physical property. This means that the charge on any object or particle cannot take arbitrary values; instead, it must always be an integral multiple of a basic, fundamental unit of charge. This fundamental unit is the magnitude of the charge of a single electron or proton.

The smallest stable, independent charge known to exist in nature is the elementary charge, denoted by the symbol e. The charge of an electron is $-e$ and the charge of a proton is $+e$.

The experimentally determined value of this fundamental constant e is approximately:
$e\approx 1.6\times {10}^{-19}\text{ Coulomb}$
Therefore, the minimum possible charge that an isolated, independent particle can carry is this elementary unit of charge, which is 1.6 x 10^-19 Coulomb.