A charge Q is placed at each of the two opposite corners of a square . A charge q is placed at each of the other two corners . If the resultant force on each charge q is zero , then

Question

$(a)\;q=2\;Q\qquad(b)\;q=-\sqrt{2}\;Q\qquad(c)\;q=2 \sqrt{2}\;Q\qquad(d)\;q=-2 \sqrt{2}\;Q$