Hydrogen atom:
The electronic ground state of hydrogen atom contains one electron in the first orbit. If sufficient energy is provided, this electron can be promoted to higher energy levels. The electronic energy of a hydrogen-like species (any atom//ions with nuclear charge Z and one electron) can be given as
`E_(n)=-(R_(H)Z^(2))/(n^(2))` where `R_(H)= "Rydberg constant," n= "principal quantum number"`
The energy required to promote the ground state electron of H-atom to the first excited state is:
When an electron returns from a higher energy level to a lower energy level, energy is given out in the form of UV//Visible radiation.

Answer

`10.2 eV`