Question

the uniform charge are placed at a distance 2 metre apart from each other the force acting between them is 16×10^9 and the distance between them is doubled then force of between them

Answer 1

I think this might be your questions answer..

Answer 2

here charges are uniform...

We know that,
force F=q1q2/r^2
:. F=q^2/r^2
given force=16×10^9
if it's on SI unit then we have to add 1/4#€ of which amount is 9×10^9
so,
16×10^9=q^2/4

now distance is doubled then the force will be
F'=q^2/(2×2)^2
=q^2/16
=1/4 q^2/4
=1/4 F
so then the force will be 1/4 of the first force...