A beam of electrons move horizontally from South to North in the region of the magnetic field acting vertically downward. The force acting on the electron due to the magnetic field is directed:

towards the east

The correct answer is Option (3) → towards the east

Magnetic force (F) on a moving charged Particle -

$\vec F=q(\vec v×\vec B)$

where,

$\vec v$ = Velocity of particle from south to north.

$\vec B$ = Magnetic field acting vertically downward.

∴ According to right hand thumb rule, the force on electron will be opposite to direction of thumb rule, which is Eastward.