Coulombs law says that the force between any two charges depends on the amount of charges and distance between them. This force is directly proportional to the magnitude of the two charges and inversely proportional to the distance between them.
where are charges,
is the distance between them and k is the coulomb constant.
case 1:
case 2
case 3:
Comparing the 3 cases:
The maximum potential force according to coulombs law is between -1 charge and +3 charge separated by a distance of 100 pm.