The correct option for the value of vapour pressure of a solution at $45^{\circ }\text{C}$ with benzene to octane in molar ratio $3:2$ is: [At $45^{\circ }\text{C}$ vapour pressure of benzene is $280\text{mm Hg}$ and that of octane is $420\text{mm Hg}$ ]

1. A
   $336\text{mm of Hg}$
2. B
   $350\text{mm of Hg}$
3. C
   $160\text{mm of Hg}$
4. D
   $168\text{mm of Hg}$