In the reversible reaction $\mathrm{A}+\mathrm{B}\to \mathrm{C}+\mathrm{D}$,the concentration of each C and D at equilibrium was 0.8 mole / liter, then the equilibrium constant ${\mathrm{K}}_{\mathrm{C}}$ will be

The reversible reaction is  $\mathrm{A}+\mathrm{B}\to \mathrm{C}+\mathrm{D}$ 

Consider the initial concentration of each A and B to be 1 mol/liter. At equilibrium, concentration of each C and D is 0.8 mol/liter. From Initial Change Equilibrium table of equilibrium,