In a hydrogen atom, the electron is at a distance of 4.76A° from the nucleus. The angular momentum of the electron is

r₀ = 0.529 A⁰

r_n = r₀ n²

given r_n = 4.76A° 

4.76 = 0.529 $\times$ n²

n² =$\frac{4.76}{0.0529} =8.99$

n² = 9

n=3

Angular momentum mvr =$\frac{\mathrm{nh}}{2\mathrm{\pi }}$ =$\frac{3\mathrm{h}}{2\mathrm{\pi }}$