The first quantum mechanical model of the atom was proposed by ........

The energy required by electrons, present in the first Bohr orbit of hydrogen atom to be excited to the second Bohr orbit is . . . . . . $J \ mol^{-1}$.
Given: $R_{H} = 2.18 \times 10^{-11} \ ergs$

What is the numerical value of angular momentum for an electron in the first orbit of a hydrogen atom? $(h = 6.626 \times 10^{-34} \ J \ s)$

In the atomic spectrum of hydrogen, the wavelengths of the spectral lines corresponding to electronic transitions $(i)$ $n=4$ to $n=2$ and $(ii)$ $n=3$ to $n=1$ are $\lambda_1$ and $\lambda_2$ $\mathring{A}$ respectively. The value of $(\lambda_1-\lambda_2)$ (in cm) is ($R_H$ = Rydberg constant)

In the hydrogen spectrum,if an electron transitions from the $6^{th}$ orbit to the $3^{rd}$ orbit,what is the total number of spectral lines produced?

If the potential energy of an electron in the second orbit of $He^+$ is $-27.2 \, eV$,then calculate the double value of the energy of the first excited state of a hydrogen atom in $eV$.