Given de- Broglie's explanation of quantisation of angular momentum as proposed by Bohr.

Explanation

According to Bohr the angular momentum of the electron is an integral multiple of `h//2pi`
i.e., `mvr=(nh)/(2pi)`
de-Broglie argued that these electrons exhibit wave property having stationary wave pattern having nodes at the ends.
The total distance travelled by a wave is an integral multiple of the wave length .
i.e., `2pir=nlambda`
`lambda=h/P=h/(mv)`
`therefore 2pir=(nh)/(mv)`
`mvr=(nh)/(2pi)`
But angular momentum of the electron is L=mvr
Hence `L=(nh)/(2pi)`