The temperature-composition phase diagram for an ideal mixture of octane $\left({\text{C}}_8{\text{H}}_{18}\right)$ and decane $\left({\text{C}}_{10}{\text{H}}_{22}\right)$ is pictured below

If the temperature of the mixture rises from ${\text{T}}_{\text{1}}{\text{ to T}}_{\text{2}}\text{,}$

Mole fraction of Octane increases in liquid phase

Mole fraction of Decane increases in liquid phase 

Mole fraction of Decane increases in vapour phase

Mole fraction of Octane increases in vapour phase