Physics - Magnetism Question with Solution | TestHub

Both straight wires point radially at the centre O, so $d\vec{\ell }\times \vec{r}=0$ and they produce no field at O.

The current i entering the loop splits equally between the two semicircular arcs (i/2 each).

The two arcs produce fields at O of equal magnitude but opposite sense (one clockwise, one anticlockwise).

Hence they cancel and B = 0 at the centre. Hence (A).