Given in the adjoining figure is a square loop PQRS made out of uniform conducting wire. If the current enters the loop at P and leaves at S, then choose the correct statement regarding the magnetic field.

Current in the circuit gets divided as shown in the diagram to maintain same voltage across P and S.
At 0 , magnetic field due to single segment, say PQ can be taken to be B. Then magnetic field due to other segments like QR and RS will also be B as same current flows through them.
Directions of magnetic field through PQ,QR and RS will be same as can be determined by right hand thumb rule.
Thus net magnetic field due to PQRS will be 3B
Since current in PS is thrice the current in PQRS, magnetic field in segment PS will also come out to be 3B but in opposite direction to magnetic field due to PQRS

Thus, ${\mathrm{B}}_0=+3\mathrm{B}-3\mathrm{B}=0$