The equilibrium constant for the given reaction H2 + I2 ⇌ 2HI is correctly
given by expression
K = ([H2] [I2]) / [HI]
K = ([H2] [I2]) / [2HI]
K = ([H2] [I2]) / [HI]2
K = [HI]2/ ([H2] [I2])
K = [HI]2[H2][I2]