An electron is in one of this electrons

The total energy of the electron in any orbit of one electron containing species is given by the expression

A physicist was performing experiments to study the velociyt and wavelength of the electron. In one case, the electron was accelerated through a potential differences of 1 KV and in second case it was accelerated through a potential difference of 2KV. The velocity acquired by the electron will be

What happens to electrostatic potential energy of a two electron system, if one electrons brought towards another electron?

Name a species which has (i) one proton and one electron (ii) one proton and two electrons