Total number of spectral lines when an electron jumps from the $8^{th}$ orbit to the $2^{nd}$ orbit is:

What is the number of photons of light with a wavelength of $4000 \ pm$ that provide $1 \ J$ of energy?

Supposing the energy (in arbitrary units) of the energy levels in the hydrogen atom is given as under:

Energy level	$K$ $(n=1)$	$L$ $(n=2)$	$M$ $(n=3)$	$N$ $(n=4...n=\infty)$
Energy	$-864 \ a.u.$	$-216 \ a.u.$	$-96 \ a.u.$	$0 \ a.u.$

The excitation energy needed to raise the electron from $M$ level to $n = \infty$ would be:

If the binding energy of electrons in a metal is $250 \ kJ \ mol^{-1}$,what should be the threshold frequency of the striking photons in order to free an electron from the metal surface?

The ratio of the wavelengths of the light absorbed by a Hydrogen atom when it undergoes $n=2 \rightarrow n=3$ and $n=4 \rightarrow n=6$ transitions,respectively,is

Bohr's model cannot explain the emission spectrum of