The radius of the second excited state of $Li^{2+}$ is ................ $\mathring{A}$.

Find out the distance between the $2^{nd}$ and $3^{rd}$ orbit of the $H^{-}$ ion.

If the first emission in the Lyman series of a hydrogen atom occurs at $121.5 \ nm$,what will be the energy difference between the first and second orbits in $kJ/mol$?

What is the maximum number of emission lines when the excited electron of an $H$ atom in $n=6$ drops to the ground state?

The energy of an electron in an orbit of a hydrogen-like ion with an orbit radius of $52.9 \ pm$ in $J$ is (ground state energy of an electron in a hydrogen atom is $-2.18 \times 10^{-18} \ J$).

Calculate the radius of the third orbit of $He^{+}$. (in $pm$)