Which of the following figures correctly describes electrorefining ?

1.

2.

3.

4.

2.

Reason — Electrolytic refining is a process by which metals containing impurities are purified electrolytically to give a pure metal. Option 2 shows the set-up used for electrolytic refining of copper:

• Anode – impure copper block (loses electrons and goes into solution).
  Cu - 2e^- ⟶ Cu²⁺
• Cathode – thin sheet of pure copper (gains mass as metal is deposited).
  Cu²⁺ + 2e^- ⟶ Cu
• Electrolyte – acidified aqueous CuSO₄ solution.

As current passes, pure copper is transferred from the impure anode to the cathode, while insoluble impurities collect below the anode as "anode mud".