This question was unpopular.  Almost all the candidates failed to include “narrow beam” in their definition of “electron gun” and so lost valuable marks.

The expected answers are:

(a)        An “electron gun” is a device that produces a narrow beam of high speed/velocity
            electrons.
e.g
(b)        -           Cathode ray tube
            -           X-ray tube
            -           Cathode ray oscilloscope
            [Accept any other correct equipment].