Benzoic acid undergoes dimerisation in benzene solution. The van’t Hoff factor (i) is related to the degree of association ‘x’ of the acid as

$$\begin{gathered} 2{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH} \to {\left({\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}\right)}_2 \\ \mathrm{Initial}: 1 - \\ \mathrm{after} \\ \mathrm{association}, 1-\mathrm{x} \mathrm{x}/2 \\ \mathrm{Total}=1-\mathrm{x}+\frac{\mathrm{x}}{2}=1-\frac{\mathrm{x}}{2} \\ \mathrm{i}=\frac{\left(1-\frac{\mathrm{x}}{2}\right)}{1}=1-\frac{\mathrm{x}}{2} \end{gathered}$$