RRB Group D 1 Dec 2025 Shift 2 Solved Paper

Concept:In electrolytic refining, the impure metal acts as the anode while a pure metal strip serves as the cathode.Explanation:Electrolytic refining purifies metals like copper, zinc, and silver using electrolysis.The anode is made of the impure metal that needs to be refined.The cathode is a thin sheet of the pure metal.The electrolyte is a soluble salt solution of the same metal, e.g., acidified copper sulfate ($\mathrm{CuSO}_4$) for copper refining.When electric current passes, the impure metal at the anode dissolves as metal ions: $\mathrm{M} \rightarrow \mathrm{M}^{n+} + n e^-$.These ions move through the electrolyte and deposit on the pure metal cathode: $\mathrm{M}^{n+} + n e^- \rightarrow \mathrm{M}$.Impurities either dissolve in the electrolyte or settle as anode mud at the bottom.Thus, only the impure metal can dissolve and allow purification.Using a graphite rod or inert electrode would not supply the metal ions needed for deposition.A pure metal strip is used as the cathode, not the anode.Therefore, the anode must be a strip of impure metal.Answer:A strip of impure metal to be refined