At $300\mathrm{K}$ pure liquid A and pure liquid B have vapour pressures $300\mathrm{torr}$ and $200\mathrm{torr}$. An equimolar liquid mixture of A and B is found experimentally to have a total vapour pressure of $215\mathrm{torr}$. Which conclusion is correct?

1. AThe mixture is ideal, with ${\Delta }_{\mathrm{mix}}H=0$
2. BNegative deviation; A-B interactions are stronger than A-A and B-B interactions, and ${\Delta }_{\mathrm{mix}}H<0$
3. CPositive deviation; A-B interactions are stronger than A-A and B-B interactions, and ${\Delta }_{\mathrm{mix}}H<0$
4. DNegative deviation; A-B interactions are weaker than A-A and B-B interactions, and ${\Delta }_{\mathrm{mix}}H>0$