The electrostatic force depends on the dielectric constant of the intervening medium. The electrostatic force is very much stronger than the gravitational force.

Why does electrostatic force depend on medium?

It is because a medium can be polarised by an external E-field. The dipoles so set up produce the external E-field produce an E-field in the opposite direction so the net E-field (the sum of the external and dipole produced E-fields) is smaller. Thus the force a given charge is smaller.

What does the electrostatic force depends on?

Answer: According to Columb's law, Electrical forces between charges depend upon Product of Magnitude of charges, distance between charges and permitivity of the medium where charges locate.