$80\mathrm{.}1gS{O}_3$ is introduced into an evacuated reaction vessel with a volume of $1d{m}^3$ at an elevated

temperature. The equilibrium mixture contains only half of the $S{O}_3$ introduced. What is the

equilibrium constant $K_c$ of the $S\frac{O_2}{S}{O}_3$ equilibrium $S{O}_2+\frac{1}{2}{O}_{2}harrS{O}_3?$