Native silver metel froms a water solube, complex with a dilute aqueous solution of `NaCN` in the presence of

Options

A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Argon

Explanation

To solve the question regarding the formation of a water-soluble complex of native silver metal with a dilute aqueous solution of sodium cyanide (NaCN), we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
Native silver (Ag) can react with sodium cyanide (NaCN) to form a soluble complex. This reaction typically occurs in the presence of oxygen.

2. **Formation of the Complex**:
When silver metal is treated with a dilute solution of NaCN in the presence of oxygen, it forms a complex known as sodium argento cyanide. The chemical reaction can be represented as:
\[ 4 \text{Ag} + 8 \text{NaCN} + 2 \text{H}_2\text{O} + \text{O}_2 \rightarrow 4 \text{NaAg(CN)}_2 + 4 \text{NaOH} \]
Here, NaAg(CN)₂ is the complex formed.

3. **Properties of the Complex**:
The complex NaAg(CN)₂ is soluble in water, which allows for the extraction of silver from its native form.

4. **Recovery of Silver**:
The silver can be recovered from this complex by reduction. A common reducing agent used for this purpose is zinc (Zn). The reaction can be simplified as:
\[ \text{NaAg(CN)}_2 + \text{Zn} \rightarrow \text{Ag} + \text{Zn(CN)}_2 + \text{Na}^+ \]
This shows that zinc reduces the silver ion back to metallic silver.

5. **Conclusion**:
Therefore, the presence of oxygen is crucial for the formation of the water-soluble complex of silver with sodium cyanide.

### Final Answer:
**Native silver metal forms a water-soluble complex with a dilute aqueous solution of NaCN in the presence of oxygen.**

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