The expression for radius of a Bohr orbit in hydrogen atom is

Expression for the radius of H-atom is:

$\mathrm{r}=\frac{{\mathrm{n}}^2{\mathrm{h}}^2}{4{\mathrm{\pi }}^2{\mathrm{mZe}}^2}=\frac{{\mathrm{n}}^2{\mathrm{h}}^2}{4{\mathrm{\pi }}^2{\mathrm{me}}^2}$

Here, r is the radius, n is the orbit number, h is the Planck's constant, m is the mass and e is the electronic charge and Z is the atomic number (Z=1) for the H atom.