Match List I with List II
| LIST I | LIST II |
| A. Zone refining | I. Dressing of ZnS |
| B. Froth Floatation process | II. Extraction of Au |
| C. Cyanide process | III. Extraction of Al |
| D. Electrolytic reduction | IV. Ultrapure Ge |
Choose the correct answers from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-IV, B-I, C-II, D-III
(A) Zone refining — This matches (IV) Ultrapure Ge. Impurities are more soluble in the melt than in the solid metal, so a moving molten zone sweeps them to one end; it gives semiconductor-grade Ge, Si, B, Ga and In.
(B) Froth floatation process — This matches (I) Dressing of ZnS. It removes gangue from sulphide ores such as ZnS (zinc blende), PbS and \( \ce{CuFeS2} \).
(C) Cyanide process — This matches (II) Extraction of Au. Gold (and silver) is leached with dilute NaCN or KCN in air and then displaced by zinc:
\( \ce{4Au + 8CN- + 2H2O + O2 -> 4[Au(CN)2]^- + 4OH-} \)
\( \ce{2[Au(CN)2]^- + Zn -> 2Au + [Zn(CN)4]^2-} \)
(D) Electrolytic reduction — This matches (III) Extraction of Al. Pure \( \ce{Al2O3} \) mixed with \( \ce{Na3AlF6} \)/\( \ce{CaF2} \) is electrolysed (Hall-Heroult process):
Cathode: \( \ce{Al^3+ + 3e- -> Al} \) Anode: \( \ce{C + 2O^2- -> CO2 + 4e-} \)
Shortcut: (A)-(IV) leaves Options (2) and (4); (C)-(II) then leaves only Option (2).
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.