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

Consider the following spectral lines for atomic hydrogen:
$A$. First line of Paschen series
$B$. Second line of Balmer series
$C$. Third line of Paschen series
$D$. Fourth line of Bracket series
The correct arrangement of the above lines in ascending order of energy is:

Number of spectral lines obtained in $He^{+}$ spectra,when an electron makes transition from fifth excited state to first excited state will be

The wave number of the first emission line in the Balmer series of the $H$ atom spectrum will be .......

$A$ certain metal has a work function of $\Phi = 2 \ eV$. It is irradiated first with $1 \ W$ of $400 \ nm$ light and later with $1 \ W$ of $800 \ nm$ light. Among the following,the correct statement is
[Given: Planck constant $(h) = 6.626 \times 10^{-34} \ J \ s$;
Speed of light $(c) = 3 \times 10^8 \ m \ s^{-1}$ ]

Find the wave number of the shortest wavelength in the Balmer series.