The group having isoelectronic species is:

The total number of orbitals associated with the principal quantum number 5 is :

A stream of electrons from a heated filament was passed between two charged plates kept at a potential difference V esu. If e and m are charge and mass of an electron, respectively, then the value of h / $$\lambda $$ (where $$\lambda $$ is wavelength associated with electron wave) is given by :

Which of the following is the energy of a possible excited state of hydrogen?