Concept:Highly reactive metals are obtained by the electrolysis of their fused salts.Explanation:Sodium is a highly reactive metal, so it cannot be obtained by chemical reduction.It is commercially extracted by the electrolysis of fused sodium chloride, NaCl, in the Downs process.Silver and copper are extracted from their ores by heating or roasting.Helium is obtained from natural gas by fractional distillation.Answer:D. Sodium