The ratio of the velocity of an electron in the second orbit of $He^{+}$ to the third orbit of $B^{4+}$ is:

Energy of an electron in the ground state of the hydrogen atom is $-2.18 \times 10^{-18} \ J$. Calculate the ionization enthalpy of atomic hydrogen in terms of $J \ mol^{-1}$.

If $P.E.$ of $3^{rd}$ shell is $-20 \ eV/atom$,then find the $I.P.$ of the $3^{rd}$ shell of that element.

If $n=2$ for $He^{+}$ ion,then what is the wavelength in $\mathring{A}$?

With increasing Principal Quantum number,the energy difference between adjacent energy levels in $H$ atom:

What is the potential energy of the electron in the $L$ shell of the hydrogen atom? (in $eV$)