Concept:Reduction is a chemical process involving the gain of electrons.Explanation:In redox reactions, oxidation means loss of electrons, while reduction means gain of electrons.This is remembered by the mnemonic OIL RIG: Oxidation Is Loss, Reduction Is Gain.Here, the process described is a gain of electrons, so it is reduction.The other options are incorrect: sublimation and distillation are physical changes, and oxidation involves loss of electrons.Answer:B. Reduction