The correct answer is C. Distillation.
Distillation is a method of separating mixtures based on their boiling points. The mixture is heated until the components with the lowest boiling points vaporize. The vapor is then condensed back into a liquid and collected.
Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei. They have the same chemical properties, but different physical properties. For example, hydrogen has three isotopes: protium, deuterium, and tritium. Protium has no neutrons, deuterium has one neutron, and tritium has two neutrons.
Isotopes can be separated by distillation because they have different boiling points. For example, water (H2O) has a boiling point of 100 degrees Celsius, while heavy water (D2O) has a boiling point of 101.4 degrees Celsius. This means that if you heat a mixture of water and heavy water, the water will vaporize first and the heavy water will vaporize later. You can then collect the vapors separately and condense them back into liquids.
The other options are not correct because they are not methods of separating mixtures based on their boiling points. Crystallization is a method of separating mixtures based on their solubilities. Sublimation is a method of separating mixtures based on their vapor pressures. Filtration is a method of separating mixtures based on their particle sizes.