A reasonably general expression for vapor-liquid phase equilibrium at low to moderate pressures is γᵥᵢₚ,ᵧ,ₚ = γₗᵢₖₓ. Where γ is a vapor fugacity coefficient, γₗ is the liquid activity coefficient, and ƒ is the fugacity of pure component i. The k-value (ƒᵧ = kₓᵪ) is therefore, in general, a function of:
(A) Temperature only
(B) Temperature and pressure
(C) Temperature, pressure, and liquid composition x
(D) Temperature, pressure, liquid composition x, and vapor composition y