`underset(("Sulphide ore")) (A) + NaCN overset ("Air") hArr underset(("Complex"))(B) +Na_(2) S overset(O_(2))rarr C`.
Composition of `B` is.

Options

A. `Na[Ag(CN)_(2)]`
B. `Na_(2)[Ag(CN)_(2)]`
C. `Na[Ag(CN)_(4)]`
D. `Na_(3)[Ag(CN)_(2)]`

Explanation

To solve the problem regarding the composition of complex B formed from the reaction of a sulphide ore with sodium cyanide (NaCN) in the presence of air, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Sulphide Ore**:
The sulphide ore mentioned in the question is likely silver sulphide (Ag₂S), which is a common sulphide ore for silver.

2. **Write the Reaction**:
The reaction between the sulphide ore (Ag₂S) and sodium cyanide (NaCN) in the presence of air can be represented as:
\[ \text{Ag}_2\text{S} + 4\text{NaCN} + \text{O}_2 \rightarrow 2\text{NaAg(CN)}_2 + \text{Na}_2\text{S} \]
Here, NaAg(CN)₂ is the complex formed (B), and Na₂S is a byproduct.

3. **Determine the Composition of Complex B**:
From the reaction, we see that the complex B is sodium dicyanoargentate(I), which has the formula:
\[ \text{NaAg(CN)}_2 \]
This indicates that for every formula unit of the complex, there is one sodium ion (Na⁺), one silver ion (Ag⁺), and two cyanide ions (CN⁻).

4. **Final Composition**:
Therefore, the composition of complex B is:
\[ \text{NaAg(CN)}_2 \]

### Conclusion:
The composition of complex B is NaAg(CN)₂.

---