For a 3S-orbital value of $\psi$  is given by following relation ${\psi }_{3s}=\frac{1}{9\sqrt{3}}{\left(\frac{1}{a_0}\right)}^{3/2}(6-6\sigma +{\sigma }^2)e^{-\sigma /2}$   where $\sigma =\frac{2r.Z}{3a_0}$  . 
What is the maximum Radial distance of node from nucleus