According to Bohr's theory,the angular momentum of an electron in the $5^{th}$ orbit is ....... (in $h/\pi$)

The energy required (in $eV$) to excite an electron of $H$-atom from the ground state to the third excited state is

What is the potential energy of the electron in the $L$ shell of the hydrogen atom? (in $eV$)

One energy difference between the states $n = 2$ and $n = 3$ is $E \ eV$,in a hydrogen atom. The ionization potential of the $H$ atom is ............. $E$.

Explain the importance and the main postulates of Planck's quantum theory.

Two electrons are revolving around a nucleus at distances $r$ and $4r$. The ratio of their time periods is