Question 3
What must be true of the components for fractional distillation to separate them?
The right answer is the one marked above.
Their boiling points must differ appreciably. That is to say their volatilities must differ, so that the vapour coming off at any temperature is richer in one component than in the others.
Components with identical boiling points would vaporise together at every temperature, and no amount of controlling the cooling would ever tell them apart.