The force between two static charges is called electrostatic force.

This force is directional proportional to the product of both charges, and

Inversely proportional to the square of the distance between them.

Let, q1 and q2 are two charges seperated by a distance r.

So, force between them is

F∝ q1q2

and F∝ 1/r²

So, F=k q1q2/r²

Here, k is proportionality constant and value of k is 1/4π∈₀