Let us assume that we are talking about graviational force of attraction.
F = G M1 M2 / d²
F is the force that one object pulls the other towards itself.
Here M1 = mass of 1st particle M2 = mass of second particle
d = distance between the two particles.
G = 6.67 * 10^-11 units [exponential -11]
This force is very less for small masses and significant for planets like Earth, Sun, moon etc.
Now, if d becomes d / 2, substitute it in the equation above, to get
F = G M1 M2 / (d/2)² = G M1 M2 / ( d² / 4 ) = GM1 M2 *4 / d²
= 4 * [G M1 M2 / d²]
So the Force has become 4 times the previous value.
If we are talking about force between electric charges, then also the same result will be observed. The new value of force will be 4 times the original value.