$\begin{align}  & \overline{x}=\frac{2+3+5+6}{4}=\frac{16}{4}=4 \\ & variance=\frac{{{(2-4)}^{2}}+{{(3-4)}^{2}}+{{(5-4)}^{2}}+{{(6-4)}^{2}}}{4} \\ & variance=\frac{4+1+1+4}{4}=\frac{5}{2} \\ & S.D=\sqrt{variance}=\sqrt{\frac{5}{2}} \\\end{align}$