How electrostatic force can be repulsive?

Dear student,

Electrostatic force is the force between the two charged particle.
The electrostatic force is attractive when the charges on the substance is different, that is one is positive and other is negative, example force between proton and electron.
The electrostatic force is repulsive when the charges on the substance is same, that is both are positive and or both are negative, example force between two protons or between two electrons.

Regards