Step-by-step explanation:
(a) An electron accelerated from rest through a potential difference of 100 V. The De Broglie wavelength in terms of potential difference is given by :

Where
m and e are the mass of and charge on an electron
Here, eV = 50 eV


The frequency of electron is given by :



(b) The mass of the proton,

The De Broglie wavelength is given by :


The frequency of proton is given by :



Hence, this is the required solution.