Question

an electron is moving along the positive x axis . you want to apply a magnetic field for a short time so that the electron may reverse its direction and move parallel to the negative x-axis this can be done by applying the magnetic field along

Answer 1

This can be done by applying magnetic field in y-axis or z-axis.

Answer 2

As long as it is perpendicular to x axis, the direction of magnetic field can be any direction.

The plane in which electron moves would only be changed otherwise it will revers the direction.

Y direction of magnetic field is required in this situation. And this idea alone will not help reverse the direction of electron. For this electric field should be made in order to pass current through a perpendicular coin which should be in the Z direction. And this will be done to make the current flow in such a direction that it interacts with the magnetic field.