Two charged objects separated by some distance attract each other. if the charges on both objects are doubled with no change in distance between them, what happens to the magnitude of the force between the objects?

The force of attraction between two charged particles is given by the Coulomb's law which may be written as,

F = k (Q1) (Q2) / (d^2)

If the charges in both are doubled, the expression would be,

F = k (2) (Q1) (2) (Q2) / (d^2)

We can conclude that by doing so, the force of attraction is multiplied by 4.