At a particular instant, an electron moves toward the east in a uniform magnetic field that is directed straight downward. the magnetic force that acts on it is

towards the south

Explanation:

When the electron enters the region with magnetic field, it experiences a magnetic force perpendicular to both the directions of the electron's velocity and the magnetic field.

The direction of the force exerted on the electron can be found by using the right-hand rule:

- Index finger: direction of the velocity of the electron - -> towards the east

- Middle finger: direction of the magnetic field - -> downward

- Thumb: direction of the force on a positive particle - -> towards the north

However, the electron is a negatively charged particle, so we must reverse the direction of the force: therefore, the force exerted on the electron is towards the south.