Hello candidate,

At each of these four corners off the square four charges are placed with charges Q and q at adjacent corners.

It's Mention that the net electrostatic force on the charge Q is zero, so upon adding all the electrostatic forces in vector addition we get the ratio of Q/q is equal to 2√2, where the formula of electrostatic force is given by kq1×q2/ r^2.

Hope this answer was helpful!!

Good luck.