Question

the minimum value of charge on any object cannot be less than

Answer 1

minimum value of charge equals charge on each electron . this values is the smallest value . we cannot get less than it.
e.g., charge on each electron = -1.6 × 10^-19C

so, -1.6 × 10^-19C is thr minimum value of charge on any object cannot be less than with it.

also you know, charge is quantised . it means charges flow from one object to another in integral number. if we say any object have 1C charge it means there are 6.25 × 10^18 electrons in that object.