4 moles of A are mixed with 4 moles of B . At equilibrium for the...

The initial concentrations of A, B, C, and D are 4M, 4M, 0M, and 0M respectively.

The equilibrium concentrations of A,B,C and D are& 4−2=2M,& 4−2=2M, 2M and 2M respectively.

$A + B ⇌ C + Dinitialconc4400atequilibrium\left(4 - 2\right)\left(4 - 2\right)22$

The expression for the equilibrium constant is $= \dfrac{[ C ] [ D ] }{[ A ] [ B ]}$

$∴ K\left(eq\right) = \dfrac{2 \times 2}{2 \times 2} = 1$