For a 3s-orbital, value of  $\mathrm{\psi }$ is given by following relation:
 $\mathrm{\psi }\left(3\mathrm{s}\right)=\frac{1}{9\sqrt{3}}{\left(\frac{1}{{\mathrm{a}}_0}\right)}^{3/2}\left(6-6\mathrm{\sigma }+{\mathrm{\sigma }}^2\right){\mathrm{e}}^{-\mathrm{\sigma }/2};\mathrm{where}\mathrm{\sigma }=\frac{2\mathrm{r}.\mathrm{Z}}{3{\mathrm{a}}_0}$
What is the maximum radial distance of node from nucleus?