State the uses of atomic spectra.

What is the experimental evidence in support of the idea that electronic energies in an atom are quantized?

When a metal surface is exposed to a certain frequency of electromagnetic radiation,the kinetic energy of the electron ejected from the metal surface is $0.20 \ eV$. If its work function $(W_0)$ is $4.80 \ eV$,the approximate frequency of the radiation falling on the metal surface in $Hz$ is:

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

With increasing Principal Quantum number,the energy difference between adjacent energy levels in $H$ atom:

The ionisation energy of a certain element is $1540 \ kJ \ mol^{-1}$. When the atoms of this element are in the first excited state,the ionisation energy is only $300 \ kJ \ mol^{-1}$. Determine the region of the electromagnetic wave spectrum in which the light is emitted during a transition from the first excited state to the ground state.