An arrangement of three parallel straight wires A, B, and C (carrying current $I$ in same direction) are placed perpendicular to the plane of paper. A and C are at a distance $d$ from B, and the angle $\angle ABC=90^{\circ }$. Magnitude of force per unit length on the middle wire ‘B’ is:

1. A
   $\frac{{\mu }_0{I}^2}{\sqrt{2}\pi d}$
2. B
   $\frac{\sqrt{2}{\mu }_0{I}^2}{\pi d}$
3. C
   $\frac{{\mu }_0{I}^2}{2\pi d}$
4. D
   $\frac{{\mu }_0{I}^2}{\sqrt{2}\pi d}$