Ammonia dissociates as follows:
NH₃(g) ⇌ 1/2N₂(g)+3/2H₂(g)
If the total pressure of the mixture is Pₜ and the degree of dissociation of NH₃ is x, then the equilibrium constant will be numerically equal to:

a. (3x/2)²
b. 4x²/(1-x)²
c. x²/(1-x)²
d. (2x/3)²