Aproton is traveling -x direction through a uniform magnetic field which is in the +x direction. in which direction will the proton be immediately pushed.

No force acts on it. It will not be pushed.

Explanation:

The proton moving in the -X direction implies its velocity is in the -X direction and the magnetic field is given to be in the +X direction. So the angle between them is 180 degrees. So no force acts on the proton, since the velocity and magnetic field are anti parallel.

Magnetic force is given by the equation F = q v B sin theta where theta is the angle between the velocity and the magnetic field. This force will be a maximum if they are perpendicular to each other.