In a hydrogen atom,electrons are excited to the $5^{th}$ quantum level. How many different spectral lines may appear in the emission spectrum?

What is the ratio of the radii of the second orbit for $H$,$He^{+}$,and $Li^{2+}$?

The work function of a metal $M$ is $6.3 \ eV$. The wavelength of the incident radiation required to just eject the electrons from its surface (in $nm$) is

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 $eV$.

The electron in a hydrogen atom,upon absorbing $12.75 \ eV$ of energy,will jump to the ....... orbit.

The angular momentum of the $2^{nd}$ Bohr orbit of the $H$ atom is $x$. Find the angular momentum of the $1^{st}$ excited state of $Li^{+2}$.