A wire in the form of a square of side $'a'$ carries a current $'i'$. Then the magnetic induction at the centre of the square is : <br> (Magnetic permeability of free space = $\mu_0$)

Question

( A ) $\frac{\mu_0 i \sqrt{2}}{\pi a}$
( B ) $\frac{2\sqrt{2}\mu_0 i}{\pi a}$
( C ) $\frac{\mu_0 i}{2\pi a}$
( D ) $\frac{\mu_0 i}{\sqrt{2}\pi a}$