Answer
Coulomb's Law is an inverse-square law, meaning the force is inversely proportional to the square of the distance.
Work Step by Step
$$F = k \frac{q_{1} \; q_{2}}{d^{2}}$$
For example, if the distance between the particles is tripled, the force is divided by a factor of 9.
On the other hand, if the two charges are brought closer together, reducing their separation distance by a factor of 3, the force is multiplied by a factor of 9.
