Charges in a Square Frame!

Given a square frame of diagonal length $2r$ made of insulating wires. There is a short dipole, having dipole moment $P$ , fixed in the plane of the figure lying at the center of the square, making an angle $\theta$ as shown in figure. Four identical particles having charges of magnitude $q$ each and alternatively positive and negative sign are placed at the four corners of the square. Select the correct alternative (s) :-

(A) Electrostatic force on the system of four charges due to dipole is $\frac{6kPq}{r^3}$

(B) Electrostatics force on the system of four charges due to dipole is $\frac{6kPq}{r^3}\cos \theta$

(C) Net torque on the system of four charges about the centre of the square due to dipole is zero

(D) Net torque on the system of four charges about the centre of the square due to dipole is $\frac{3kPq}{r^2}$