A square loop of side 2a , and carrying current i, is kept in XZ plane with its center at origin . A long wire carrying the same current i is placed parallel to the z-axis and passing through the point (0, b, 0) , (b > > a ) the magnitude of the torque on the loop about Z-axis  is given by :

• A

  $\frac{\text{2}{\mu }_{\text{0}}{\text{I}}^{\text{2}}{\text{a}}^2}{\text{πb}}$

• B

  $\frac{{\mu }_{\text{0}}{\text{I}}^{\text{2}}{\text{a}}^{\text{3}}}{{\text{2πb}}^{\text{2}}}$

• C

  $\frac{\text{2}{\mu }_{\text{0}}{\text{I}}^{\text{2}}{\text{a}}^{\text{3}}}{{\text{πb}}^{\text{2}}}$

• D

  $\frac{{\mu }_{\text{0}}{\text{I}}^{\text{2}}{\text{a}}^2}{\text{2πb}}$