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

Options

A. displacement of metal by some other 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 by leaching with cyanide ions (CN⁻). This process involves dissolving the metals in a solution containing cyanide, forming a soluble complex.

2. **Formation of Metal-Cyanide Complex:**
- When silver (Ag) or gold (Au) is treated with cyanide, it forms a complex. For example, silver forms the complex Na₃[Ag(CN)₂]. This complex is soluble in water.

3. **Recovery of the Metal:**
- To recover the metal from the cyanide complex, a method called displacement is used. This involves using a more reactive metal to displace the silver or gold from the complex.

4. **Using Zinc for Displacement:**
- Zinc (Zn) is commonly used for this purpose. When zinc is added to the silver cyanide complex, it displaces silver from the complex, resulting in the formation of zinc cyanide and free silver metal.

5. **Chemical Reaction:**
- The reaction can be represented as follows:
\[ \text{Na}_3[\text{Ag(CN)}_2] + \text{Zn} \rightarrow \text{Ag} + \text{Na}_2[\text{Zn(CN)}_4] \]
- In this reaction, zinc replaces silver in the complex, allowing silver to precipitate out.

6. **Conclusion:**
- The correct method for recovering gold and silver from their cyanide complexes is through the displacement of the metal by another metal, specifically zinc.

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

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