A straight wire carrying current is parallel to the y-axis as shown in figure. The

detailed solution

Correct option is B

The direction of the magnetic field is perpendicular to the plane containing the point P and the current element I, which is the z-direction. Hence choice (a) is wrong and choice (b) is correct. Also the fields to the left and to the right of the current element are oppositely directed. Hence choice (d) is correct. Further, the lines of force of the magnetic field are concentric circles with their common centre at the wire. Hence choice (c) is also correct.