Step-by-step explanation:
It is given that,
Speed of the electron in horizontal region,

Vertical force,

Vertical acceleration,

..........(1)
Let t is the time taken by the electron, such that,


...........(2)
Let
is the vertical distance deflected during this time. It can be calculated using second equation of motion:

u = 0



So, the vertical distance the electron is deflected during the time is 0.426 mm. Hence, this is the required solution.