The correct answer is: Electric Potential
Step-by-step explanation:
It cannot be electric potential energy because as the positive charge is attracting the negative charge and you are moving away from the positive charge (as the distance increases), it means you are doing the positive work. Therefore, the electric potential energy will increase. Electric charge, the fourth option, will remain constant due to the conservation of charge. Potential difference has nothing to do with distance (considering the current situation).
Now let us talk about the electric potential!
As our reference point in this case is the positive charge (Q), the electric potential w-r-t that (Q) is:
V = kQ/r
Where V is the electric potential. As you are moving away from (Q), the electric potential will decrease as r (distance between q and Q) will increase. Hence, the correct answer is: Electric potential!