Which one of the following is incorrect for ideal solution? 

$\text{ For an ideal solution, }{\mathrm{\Delta H}}_{mix}=0,{\mathrm{\Delta V}}_{mix}=0,$

$\begin{array}{l}\text{ Now, }{\mathrm{\Delta U}}_{\text{mix }}={\mathrm{\Delta H}}_{\text{mix }}-{\mathrm{P\Delta V}}_{\text{mix }}\\ \therefore {\mathrm{\Delta U}}_{\text{mix }}=0\end{array}$

$\mathrm{Also},\mathrm{for} \mathrm{an} \mathrm{ideal} \mathrm{solution},$

${\mathrm{p}}_{\mathrm{A}}={\mathrm{x}}_{\mathrm{A}}{\mathrm{p}}_{\mathrm{A}}°,{\mathrm{p}}_{\mathrm{B}}={\mathrm{x}}_{\mathrm{B}}{\mathrm{p}}_{\mathrm{B}}°$

$\therefore \mathrm{\Delta P}={\mathrm{P}}_{\text{obs }}-{\mathrm{P}}_{\text{calculated by }}=0$

${\mathrm{\Delta G}}_{mix}={\mathrm{\Delta H}}_{mix}-{\mathrm{T\Delta S}}_{mix}$

$\text{ For an ideal solution, }{\mathrm{\Delta S}}_{mix}\ne 0$

$\therefore {\mathrm{\Delta G}}_{\mathrm{mix}}\ne 0$