In another case you want to study a fractionation column, which separates a series of hydrocarbons based on different carbon numbers. Which of the following thermodynamic model is suitable?

$($A$)$ Redlich$-$Kwong equation of state

$($B$)$ NRTL

$($C$)$ UNIQUAC

$($D$)$ UNIFAC

Regarding the UNIFAC model, which of the following statement is true?

$($A$)$ This model is commonly used to estimate the pure component properties.

$($B$)$ This model is not applicable to those compounds, whose structure cannot be divided into the pre$-$defined functional groups.

$($C$)$ This model is essentially an equation$-$of$-$state based model.

$($D$)$ The relative solubility $(R_k)$ and the relative charge $(Q_k)$ for the functional groups are essential for the UNIFAC model.