Extraction of gold and silver involves leaching the metal with `CN^(-)` ion. The metal is recovered by _______

Options

A. displacement of metal by some metal from the complex ion.
B. roasting of metal complex
C. calcination followed by roasting
D. thermal decomposition of metal complex

Explanation

**Step-by-Step Solution:**

1. **Understanding the Process of Leaching:**
- Gold and silver are extracted from their ores using a process called leaching, where the metal is dissolved in a solution containing cyanide ions (CN^-). This forms a soluble complex with the metal.

2. **Formation of Metal-Cyanide Complex:**
- When gold (Au) or silver (Ag) is treated with cyanide ions, a complex ion is formed. For example, the reaction for gold can be represented as:
\[ \text{Au} + \text{CN}^- \rightarrow \text{[Au(CN)₂]}^- \]
- This complex is soluble in water, allowing for the separation of the metal from its ore.

3. **Recovery of the Metal:**
- To recover the gold or silver from the cyanide complex, a reducing agent is used. In this case, zinc (Zn) is commonly employed. The reaction can be represented as:
\[ \text{[Au(CN)₂]}^- + \text{Zn} \rightarrow \text{Au} + \text{[Zn(CN)₄]}^{2-} \]
- Here, zinc displaces gold from the complex, leading to the formation of solid gold and a new zinc-cyanide complex.

4. **Conclusion:**
- The metal (gold or silver) is recovered by the displacement of the metal from the complex ion using zinc. Therefore, the correct answer to the question is:
- **Displacement of metal by some metal from the complex ion.**

**Final Answer:**
The metal is recovered by **displacement of metal by some metal from the complex ion.**

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