In the leaching of `Ag_(2)S` with `NaCN`, a stream air is also passed. It is because of

Options

A. Reversible nature of reaction between `Ag_(2)S` and `NaCN`
B. Oxidised `Na_(2)S` formed into `Na_(2)SO_(4)`
C. Irreversible nature of reaction between `Ag_(2)S` and `NaCN`
D. None of above

Answer

### Step-by-Step Solution:

1. **Understanding the Reaction**: The leaching of silver sulfide (Ag₂S) with sodium cyanide (NaCN) involves a chemical reaction where silver sulfide reacts with sodium cyanide to form sodium sulfide (Na₂S) and silver cyanide (AgCN). The reaction can be represented as:
\[ \text{Ag}_2\text{S} + 4\text{NaCN} \rightarrow 2\text{AgCN} + \text{Na}_2\text{S} \]

2. **Reversibility of the Reaction**: The reaction between silver sulfide and sodium cyanide is a reversible process. This means that the products (sodium sulfide and silver cyanide) can react to form the reactants (silver sulfide and sodium cyanide) again under certain conditions.

3. **Role of Air in the Reaction**: To drive the reaction towards the formation of products and prevent the backward reaction, a stream of air is passed through the mixture. The air provides oxygen, which is essential for the oxidation of sodium sulfide (Na₂S) to sodium sulfate (Na₂SO₄).

4. **Oxidation Reaction**: The oxidation of sodium sulfide occurs as follows:
\[ 2\text{Na}_2\text{S} + 3\text{O}_2 \rightarrow 2\text{Na}_2\text{SO}_4 \]
This reaction consumes sodium sulfide and produces sodium sulfate, effectively removing sodium sulfide from the equilibrium of the original leaching reaction.

5. **Preventing Backward Reaction**: By oxidizing sodium sulfide to sodium sulfate, the concentration of sodium sulfide is reduced, which shifts the equilibrium of the original reaction to the right, favoring the formation of more silver cyanide and preventing the backward reaction from occurring.

### Conclusion:
In summary, the stream of air is passed during the leaching of Ag₂S with NaCN to oxidize sodium sulfide to sodium sulfate, which prevents the backward reaction and drives the process towards the formation of silver cyanide.

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