Question

what is distillation? the combination of substances by cooling the separation of substances by boiling point the combination of substances by mixing the separation of substances by centrifuge

Explanation:

Distillation is a separation process. It works based on the difference in boiling points of substances. When a mixture is heated, the component with the lower boiling point vaporizes first. Then, this vapor is cooled and condensed back into a liquid, thus separating it from the other components in the mixture. The option "the separation of substances by boiling point" correctly describes this process. The other options are incorrect: "the combination of substances by cooling" is not distillation (distillation is separation, not combination); "the combination of substances by mixing" is also wrong as it's about combination instead of separation; "the separation of substances by centrifuge" refers to a different separation method (centrifugation uses centrifugal force, not boiling point differences).

Answer:

the separation of substances by boiling point