An electron enters a uniform magnetic field at right angles to it as shown in the figure below. In which direction will this electron move? State the rule applied by you in finding the direction of motion of the electron.

(N/A) The electron will move perpendicular to the plane of the paper and downwards.
Explanation:
$1$. The direction of the magnetic field is towards the right.
$2$. The electron is moving upwards. Since the current is defined as the flow of positive charges,the direction of conventional current is opposite to the direction of the electron's motion,i.e.,downwards.
$3$. Applying Fleming's Left-Hand Rule: Stretch the thumb,forefinger,and middle finger of the left hand such that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field (right) and the middle finger points in the direction of the current (downwards),then the thumb points in the direction of the force acting on the electron.
$4$. According to this rule,the force on the electron acts perpendicular to the plane of the paper and downwards.