The electrostatic force between the two charges is
[tex]F=k_E \frac{q_1 q_2}{r^2} [/tex]
where q1 and q2 are the magnitudes of the two charges, and r the distance between them.
We can see from the formula that F is proportional to the product between the two charges:
[tex]F \sim q_1 q_2[/tex]
so, if the magnitude of each charge is doubled, the new force will get a factor 4:
[tex]F' \sim (2 q_1 )(2 q_2 )=4 q_1 q_2 =4 F[/tex]
So, the new force will be 4 times the original force:
[tex]F' = 4 \cdot 1N= 4N[/tex]
