State and explain coulomb's inverse square law in electricity

Statement : The electrostatic force of attraction (or) repulsion between two point sized stationary electric charges is directly proportional to product of their charges and inversly proportional to square of distance between them and acts along the line joining them.
Explanation : Let Q₁ & Q₂ are the charges seperated by a distance 'r', then electrostatic force between them is given by

$\mathrm{F}\propto \frac{{\mathrm{Q}}_1{\mathrm{Q}}_2}{{\mathrm{r}}^2}$
$\mathrm{F}=\mathrm{K}\frac{{\mathrm{Q}}_1{\mathrm{Q}}_2}{{\mathrm{r}}^2}$
The value of k is $\mathrm{K}=\frac{1}{4{\mathrm{\pi ϵ}}_0}$
where ${\in }_0$ is permitivity of free spaced
$\mathrm{F}=\frac{1}{4{\mathrm{\pi ϵ}}_0}\frac{{\mathrm{Q}}_1{\mathrm{Q}}_2}{{\mathrm{r}}^2}$
if two charges are kept in medium
$\mathrm{F}=\frac{1}{4\mathrm{\pi }\in }\frac{{\mathrm{Q}}_1{\mathrm{Q}}_2}{{\mathrm{r}}^2}$
where $\in$ is permitivity of medium.