The correct answer is option 4: fractional distillation.

Distillation is a commonly used method for separating mixtures based on differences in boiling points. In this case, the mixture of acetone and alcohol can be separated by using fractional distillation.

During the process of fractional distillation, the mixture is heated until it reaches its boiling point. The components with lower boiling points vaporize first, while the components with higher boiling points remain in the liquid phase. The vaporized components are then collected and condensed back into a liquid form.

In the case of acetone and alcohol, acetone has a lower boiling point than alcohol. Therefore, when the mixture is heated, acetone vaporizes first and can be collected separately from alcohol, which remains in the liquid phase.

Filtration (option 1) is used to separate solid particles from a liquid, so it is not suitable for separating a mixture of liquids. Separating funnel (option 2) is used to separate immiscible liquids with different densities and solubilities. Fractional crystallization (option 3) is used to separate a solid compound from a liquid mixture by allowing the compound to crystallize out. Neither of these methods is appropriate for separating acetone and alcohol.