Hey,

It is given that

Force in air that is Fa=5000N

Force in medium that is Fm=2000N

we know that

The electric force between point charges in the presence of medium is given by

Fm=Fa/e where e is the dielectric constant.

thus dielectric constant of the medium e=Fa/Fm

e=5000/2000=

which is the required answer.

I hope this helps.

All the best!