Magnetic Field

If the current flows out of the paper, the magnetic field at points to the right of the wire will be upwards and to the left will be downwards as shown in figure
Now, let us come to the problem.
Magnetic field at C = 0
Magnetic field in region BX ' will be upwards (+ve) because all points lying in this region are to the right of both the wires
Magnetic field in region AC will be upwards (+ve), because points are closer to A, compared to B. Similarly magnetic field in region BC will be downwards (-ve).
Graph (b) satisfies all these conditions. Therefore, correct answer is (b).

The magnetic field is perpendicular to the plane of the paper. Let us consider two diametrically opposite elements. By Fleming's Left hand rule on element AB the direction of force will be Leftwards and the magnitude will be

On element CD, the direction of force will be towards right on the plane of the papper and the magnitude will be dF = Id/B.