Explanation:
(A) Q, R The magnetic field at point P, due to upper wire is into the plane of paper and due to lower wire is out of the plane of paper. Hence both fields are in opposite direction & net field is zero.
(B) P The magnetic field at P will be along the axis towards right side. Hence magnetic field in the same direction due to both wire.
(C) Q, R The magnetic field due to current in the left side loop of P is equal and opposite to magnetic field due to current in right side loop hence net magnetic field = 0
(D) Q The magnetic field at P due to the currents in the wires are in opposite direction.
Hence
A → Q, R
B → P
C → Q, R
D → Q