The acceleration of the electron is (e) into the page. This is because when a charged particle moves through a magnetic field at a perpendicular angle, it experiences a force perpendicular to both the direction of motion and the magnetic field direction. In this case, the electron is moving to the right in the plane of the page while the magnetic field is going into the page. Therefore, the force experienced by the electron is directed into the page, causing it to accelerate in that direction.
Hi! When an electron moves at a constant speed in the plane of the page and enters a magnetic field going into the page, the acceleration of the electron is (a) upward, due to the interaction between its charge and the magnetic field according to the Lorentz force.