The wave function $\left(\mathrm{\psi }\right)$ of 2s is given by ${\mathrm{\psi }}_{2\mathrm{s}}=\frac{1}{2\sqrt{2}\mathrm{\pi }}{\left(\frac{1}{{\mathrm{a}}_0}\right)}^{1/2}\left(2-\frac{\mathrm{r}}{{\mathrm{a}}_0}\right){\mathrm{e}}^{-\mathrm{r}/2{\mathrm{a}}_0}$

AT $r=r_o$, radial node is formed. Thus, $r_o$ in terms of $a_o$