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

Explanation

The condition for stationary wave formation is that the total distance travelled between the nodes (two) up and down or given path is integral multiple of `'lamda'`
i.e., `2pir_(n)=nlamda` where n, 1,2,3 ........
but `lamda =(h)/(mv) ` (from de - Broglie's hypothesis)
`:. 2pr_(n)=(nh)/(mv_(n))`
i.e., `mv_(n)r_(n)=n((h)/(2pi))`
i.e., integral multiple of `((h)/(2pi))` should be equal to the angular momentum of electron in the orbit.