Iron catalyst is used in

Options

A. Contact process
B. Ostwald's process
C. Birkland - Eyde process
D. Haber's process

Answer

**Step-by-Step Solution:**

1. **Identify the Processes:**
We are given four processes to evaluate:
- Contact Process
- Ostwald Process
- Brin Process
- Haber Process

2. **Analyze Each Process:**
- **Contact Process:** This process is used for the preparation of sulfuric acid (H₂SO₄). The catalyst used here is vanadium pentoxide (V₂O₅).

- **Ostwald Process:** This process is used for the preparation of nitric acid (HNO₃). The catalysts used are platinum or rhodium.

- **Brin Process:** This is another method for the preparation of nitric acid (HNO₃), which also uses platinum as a catalyst.

- **Haber Process:** This process is used for the synthesis of ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂). The catalyst used in this process is spongy iron.

3. **Determine the Correct Option:**
From the analysis, we see that the only process that uses iron as a catalyst is the Haber Process.

4. **Conclusion:**
Therefore, the correct answer to the question "Iron catalyst is used in" is the **Haber Process**.