Which one of the following mixtures can be separated into pure components by fractional distillation?

The correct option is A

Benzene-toluene

Benzene-toluene mixture can be separated into pure components by fractional distillation. The other components are soluble in water and acids become concentrated when water is added to them. So, since the solutions formed will have almost homogenous properties. Its not possible to separate the other mixtures as their difference in boiling points are not varying by a lot.