When equal amounts of $\text{H}_2$ and $\text{I}_2$ are allowed to react, the mole fraction of HI in the equilibrium mixture is $x$. What is the value of the equilibrium constant, $K_p$, for the reaction?
- A$\dfrac{x^2}{(1-x)^2}$
- B$\dfrac{x^2}{(1-2x)^2}$
- C$\dfrac{4x^2}{(1-x)^2}$
- D$\dfrac{4x^2}{(1-2x)^2}$