Between like charges force is repulsive and between unlike charges it is attractive.

Charge Distribution in Equilateral Triangle

When three charges -q, q, and q are kept at the vertices of an equilateral triangle, the charge distribution is symmetric, and the electric field at the center is zero.

Force on Charge -q

The force acting on charge -q due to the other two charges q and q is equal in magnitude and opposite in direction. Therefore, the net force on charge -q is zero.

Force on Charge +q

The force acting on charge +q due to the other two charges q and -q is not zero. The net force on charge +q is the vector sum of the forces due to the other two charges.

Using Coulomb's law, we can calculate the magnitude of the force on charge +q.

F = kq^2/r^2

where k is the Coulomb constant, q is the charge on each particle, and r is the distance between the charges.

Since the charges are placed at the vertices of an equilateral triangle, the distance between any two charges is the same and is equal to the side length of the triangle.

r = s

where s is the side length of the equilateral triangle.

The force on charge +q due to the charge -q is attractive, and the force on charge +q due to the charge q is repulsive. Therefore, the net force on charge +q is the vector difference of the two forces.

F_net = F_repulsive - F_attractive

F_net = (kq^2/s^2) - (kq^2/(2s)^2)

F_net = (kq^2/s^2) - (kq^2/4s^2)

F_net = (3kq^2/4s^2)

F_net = (3/4)F

The net force on charge +q is (3/4) times the force acting on charge -q.

Since the force acting on charge -q is F, the force acting on any of the plus q is (3/4)F.

Therefore, the correct answer is F/√3.