Answer:
(e) The particles move apart with a velocity that increases for a while and then becomes constant.
Explanation:
Each particle feels a repulsive (because they have same sign of charge) electric force from the each other:
and
So each particle feels a repulsive force proportional to the quadratic inverse of the distance.that means that the charges begin to move away, and the further away they are from each other, the force (and therefore the acceleration) decreases, at a rate inversely proportional to the square of the distance. Theoretically this acceleration will never be zero, but in practice it will at some point reach a value very close to zero. Then the speed will grow for a while and when the acceleration has reached almost zero, the speed will practically remain constant.