Calculate the wave number of a photon emitted during the transition from the orbit $n = 2$ to $n = 1$ in a hydrogen atom $(R_{H} = 109677 \ cm^{-1})$. (in $cm^{-1}$)

The ratio of the radius of the $2^{nd}$ orbit of $H$ to the radius of the $3^{rd}$ orbit of $He^{+}$ is ......

The energy of an electron revolving in the $n^{th}$ Bohr's orbit of an atom is given by the expression

Which orbit of $Be^{+3}$ has the same orbit radius as that of the ground state of hydrogen atom?

What is the maximum number of different spectral lines obtained when a sample of a large number of $H$-atoms in the $5^{th}$ excited state makes transitions to the ground state,given that no lines are emitted in the Balmer series?

When an electron moves from $L$-shell to $M$-shell,then it will be accompanied by :