(d) May increase or decrease.The electric potential energy, E, between the two charges, q1​  and q2​ , separated by the distance, r, is given as E=K(q1​q2​)/r ,Where k = constant As the distance between the charges is increased, the energy will decrease if both the charges are of similar nature. But if the charges are oppositely charged, the energy will become less negative and, hence, will increase.