The angular  momentum  of an electron  in a given stationary  state  can be expressed  as ${\mathrm{m}}_{\mathrm{e}}\mathrm{vr}=\mathrm{n}\frac{\mathrm{h}}{2\mathrm{\pi }}$. Based  on this expression  an electron can  move  only in those orbits for which its angular  momentum is

We know that the number of orbits and their place around the nucleus is fixed. We also know that electrons can jump from one orbit to another orbit by emission or absorption of light energy. So their angular momentum must be quantized.
So an electron can revolve around a nucleus in only those orbits for which angular momentum of the electron is an integral multiple of${\displaystyle \frac{h}{2\pi }}$ . Therefore n can be an integer such as 1,2,3 and so on.