During electrolytic refining of copper, some metals settle as anode mud. These metals are:
A. Selenium and Tellurium
B. Silver and Gold
C. Gold and Platinum
D. Zinc and Platinum
E. Selenium, Gold and Platinum
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, B, C and E only
In the electrolytic refining of copper, impure (blister) copper is the anode, a thin sheet of pure copper is the cathode, and acidified \( \ce{CuSO4} \) is the electrolyte:
\( \displaystyle \text{Anode:}\ \ \ce{Cu -> Cu^2+ + 2e^-}\qquad \text{Cathode:}\ \ \ce{Cu^2+ + 2e^- -> Cu} \)
Metals that are less reactive than copper (or present as compounds such as selenides and tellurides) do not dissolve; they fall below the anode as anode mud: antimony, selenium, tellurium, silver, gold and platinum. Metals more reactive than copper, such as zinc and iron, dissolve and stay in the solution.
(A) Selenium and Tellurium — Correct. They are present in blister copper as selenides and tellurides, which do not dissolve at the anode, so both settle in the anode mud.
(B) Silver and Gold — Correct. Both are noble metals, less reactive than copper, so they are not oxidised at the anode and fall into the mud.
(C) Gold and Platinum — Correct. Both are noble metals, less reactive than copper, so they also fall into the mud.
(D) Zinc and Platinum — Incorrect. Zinc is more reactive than copper (E° = −0.76 V), so it dissolves as \( \ce{Zn^{2+}} \) and does not settle in the mud.
(E) Selenium, Gold and Platinum — Correct. All three are in the anode mud.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Electrolytic Refining – “In this method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic ones go to the anode mud. … Copper is refined using an electrolytic method. Anodes are of impure copper and pure copper strips are taken as cathode. … Impurities from the blister copper deposit as anode mud which contains antimony, selenium, tellurium, silver, gold and platinum; recovery of these elements may meet the cost of refining.”