A proton is traveling south as it enters a region that contains a magnetic field. The proton is deflected downward toward the earth. What is the direction of the magnetic field

The direction of the magnetic field is WEST.

Explanation:

Imagine that you will be heading down to Earth. That's you get a program vision of the proton's original movement. The proton arrives from the south journeying north. The magnetic field diverts it toward Earth downwards.

To follow this the field should work at the right angles to the particle's movement. In other terms the field has to behave as E-W or W-E. The filed will move from East to West using Fleming's left hand rule and understanding that the travelling proton is like a traditional current.