A current i is flowing in a hexagonal coil of side / [Fig.]. The magnetic induction at the centre of the coil will be

• A

  $\frac{\sqrt{3}{\mathrm{\mu }}_0\mathrm{i}}{\mathrm{\pi l}}$

• B

  $\frac{{\mathrm{\mu }}_0\mathrm{i}}{\sqrt{3}\mathrm{\pi l}}$

• C

  $\frac{{\mathrm{\mu }}_0\mathrm{i}}{3\sqrt{3}\mathrm{\pi l}}$

• D

  $\frac{3\sqrt{3}{\mathrm{\mu }}_0\mathrm{i}}{\mathrm{\pi l}}$