Two point charges, one q and the other – q, form a dipole separated by a distance d. A third charge Q is placed midway between these two charges. If the distance between q and – q is then doubled with the Q staying midway between the other two, what happens to the force on Q?

it will reduce by 4

Explanation:

From Coulomb's law,

Force is inversely proportional to distance of separation between the centre of the two charges.

when d is doubled, the force between q and -q will reduce by a factor of 4 same also applies to the force on Q and any of q or -q

b would be the answer

a is the best answer your welcome