A circular coil is in y-z plane with centre at origin. The coil is carrying a constant current. Assuming direction of magnetic field at x = – 25 cm to be positive direction of magnetic field, which of the following graphs shows variation of magnetic field along x-axis

Direction of magnetic field at every point on axis of a current carrying coil remains same though magnitude varies. Hence magnetic induction for whole of the x-axis will remain positive.
Therefore, (3) and (4) are wrong.
Magnitude of magnetic field will vary with x according to law, 

 .
Hence, at  

and when  

Slope of the graph will be 

 .
It means, at x = 0, slope is equal to zero or tangent to the graph at x = 0, must be parallel to x-axis.
Hence (2) is correct and (1) is wrong