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

Options

A. Ferromagnetic
B. Paramagnetic
C. Linear complex
D. Coordinate number of central atom is `4`

Explanation

To solve the question regarding the complex B formed from the reaction of a sulfide ore with NaCN in the presence of air, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Sulfide Ore (A)**:
- The sulfide ore in question can be represented as Ag₂S (Silver Sulfide).

2. **Reaction with Sodium Cyanide (NaCN)**:
- When Ag₂S reacts with NaCN in the presence of air, it forms a complex. The reaction can be represented as:
\[ \text{Ag}_2\text{S} + 4\text{NaCN} + \text{O}_2 \rightarrow 2\text{Na}_2\text{[Ag(CN)}_2\text{]} + \text{Na}_2\text{S} \]
- Here, the complex formed is \(\text{Na}_2\text{[Ag(CN)}_2\text{]}\).

3. **Determine the Nature of Complex B**:
- The complex B is \(\text{[Ag(CN)}_2\text{]}^{−}\).
- The oxidation state of silver (Ag) in this complex is +1, and it is coordinated with two cyanide (CN) ligands.

4. **Analyze the Magnetic Properties**:
- The electronic configuration of Ag in its +1 oxidation state is \([Kr] 4d^{10}\).
- Since there are no unpaired electrons in the \(4d^{10}\) configuration, the complex is diamagnetic.

5. **Identify the Coordination Number**:
- In the complex \(\text{[Ag(CN)}_2\text{]}\), silver is coordinated to two cyanide ligands, giving it a coordination number of 2.

6. **Conclusion**:
- Based on the analysis, complex B is a linear complex with a coordination number of 2 and exhibits diamagnetic properties.

### Answer:
B is a **linear complex**.