Match List I with List II
| List I | List II |
| A. \(4M + 8CN^- + 2H_2O + O_2 \overset{\Delta }{\longrightarrow} 4[M(CN)_2]^- + 4OH^-\) | I. Roasting |
| B. \(Al_2O_3 + 2NaOH + 3H_2O\overset{\Delta }{\longrightarrow} 2Na[Al(OH)_4]\) | II. Leaching |
| C. \(PbS \overset{\Delta }{\longrightarrow} PbO\) | III. Cyanide process |
| D. \(Cu_2S \overset{\Delta }{\longrightarrow} Cu\) | IV. Self reduction |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-III, B-II, C-I, D-IV
(A) 4M + 8CN− + 2H2O + O2 → 4[M(CN)2]− + 4OH− — This matches (III) Cyanide process. Silver or gold is leached with dilute NaCN/KCN in the presence of air; the metal is then displaced by zinc:
\( \ce{2[M(CN)2]^- + Zn -> [Zn(CN)4]^2- + 2M} \)
(B) Al2O3 + 2NaOH + 3H2O → 2Na[Al(OH)4] — This matches (II) Leaching. Bauxite dissolves in hot NaOH and the impurities are left behind.
(C) PbS → PbO — This matches (I) Roasting. The sulphide ore is heated in a regular supply of air below its melting point:
\( \ce{2PbS + 3O2 -> 2PbO + 2SO2} \)
(D) Cu2S → Cu — This matches (IV) Self reduction. In the converter part of \( \ce{Cu2S} \) is oxidised to \( \ce{Cu2O} \), which then reacts with the remaining \( \ce{Cu2S} \); no outside reducing agent is used:
\( \ce{2Cu2O + Cu2S -> 6Cu + SO2} \)
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.