Calculate the radius of the fourth orbit of the $B^{4+}$ ion. (in $pm$)

If a hydrogen atom is excited by an energy of $8.4 \ eV$,what will be the number of spectral lines emitted?

The frequency of radiation emitted when the electron falls from $n = 4$ to $n = 1$ in a hydrogen atom will be (Given ionization energy of $H = 2.18 \times 10^{-18} \ J \ atom^{-1}$ and $h = 6.625 \times 10^{-34} \ Js$)

What is the radius of the fourth orbit of a hydrogen atom (in $pm$)?

What will be the ratio of the wavelength of the third line of the Balmer series in the $He^{+}$ ion spectrum to the first line of the Balmer series in the $Li^{2+}$ ion spectrum?

An atom has $x$ energy levels,then the total number of spectral lines in its emission spectrum is given by: