"No two electrons in an atom can have the identical set of four quantum numbers." The statement is known as

Calculate the energy associated with third orbit of $\mathrm{He}^{+}$.

What is the wavenumber of the photon emitted during transition from the orbit $\mathrm{n}=5$ to that of $\mathrm{n}=2$ in hydrogen atom? $\left[\mathrm{R}_{\mathrm{H}}=109677 \mathrm{~cm}^{-1}\right]$