Bohr's radius can have

What is the wave number of a photon emitted during the transition from orbit $n=4$ to $n=2$ in a hydrogen atom (in $cm^{-1}$)? $[R_{H}=109677 \ cm^{-1}]$

If the shortest wavelength of the Lyman series of the $H$ atom is $x$,then calculate the total energy of the $H$ atom in the first excited state.

What is the maximum wavelength line in the Lyman series of $He^{+}$ ion?

When a hydrogen atom (ionization energy $13.6 \ eV$) jumps from the third excited state to the first excited state,the energy of the emitted photon in this process is .............. $eV$.

The kinetic energy of an electron in the second Bohr orbit of a hydrogen atom is = ....... (Bohr radius $a_0$)