If the radius of the first orbit of the $H$ atom is $a_0$, then the de Broglie wavelength of the electron in the third orbit will be ....... (in $\pi a_0$)

What is the de-Broglie wavelength of an electron,in a hydrogen atom,moving in an orbit having a maximum magnetic quantum number $m = +2$ in units of $\mathring{A}$?

If the de Broglie wavelength of the electron in the $n^{th}$ Bohr orbit in a hydrogenic atom is equal to $1.5 \, \pi \, a_0$ ($a_0$ is Bohr radius),then the value of $n/Z$ is:

What should be the momentum (in $g \ cm / s$) of a particle if its de Broglie wavelength is $1 \ \mathring{A}$ and the value of $h$ is $6.6252 \times 10^{-27} \ erg \ s$?

The de-Broglie wavelength of a particle with mass $1 \, g$ and velocity $100 \, m/sec$ is

State the de-Broglie principle and explain it.