The angular momentum of the orbital electron is integral multiple of:

According to Bohr''s second postulate, an electron can only revolve in those nuclear orbits of principal quantum numbers ''n'' which have angular momentum value as equal to integral multiples of $\frac{\mathrm{h}}{2\mathrm{\pi }}.$

Therefore, $mvr=\frac{n\mathrm{h}}{2\mathrm{\pi }}$