Four charges q , -q , q , -q are placed in order on the four consecutive corners of a square of side a . The work done in interchanging the positions of any two neighbouring charges of the opposite sign is

Question

$(a)\;\large\frac{k\;q^2}{a}\;(-4+\sqrt{2})\qquad(b)\;\large\frac{k\;q^2}{a}\;(4+2 \sqrt{2})\qquad(c)\;\large\frac{k\;q^2}{a}\;(4-2 \sqrt{2})\qquad(d)\;\large\frac{k\;q^2}{a}\;(4+\sqrt{2})$