The difference between the radii of $n^{\text{th }}$ and $(n+1{)}^{th}$ orbits of hydrogen atom is equal to the radius of $(\mathrm{n}-1{)}^{\mathrm{th}}$ orbit of hydrogen. The angular momentum of the electron in the ${\mathrm{n}}^{\mathrm{th}}$ orbit is$\_\_\_\_\_\_$($h$ is Planck's constant)