What is the definition of fractionation in the context of liquids?

Fractionation refers to the process of separating a liquid mixture into its individual components based on differing properties, such as boiling points. In the context of liquids, it usually involves the preferential evaporation of specific components, allowing them to be collected separately as they change from liquid to vapor and then back to liquid during condensation. This is commonly used in industrial processes, such as the distillation of crude oil into its various fractions, or in the separation of refrigerants during recovery and recycling.

The other options describe processes that do not accurately represent fractionation. For instance, mixing liquids for enhanced properties does not involve separation but rather the combination of substances. Similarly, combining two liquids into a single phase implies a mixing process rather than a separation one. Lastly, the solidification of a liquid into a crystalline form pertains to freezing or crystallization, which is fundamentally different from the principles of fractionation that center around separation based on vaporization.