When potassium ferrocyanide crystals are heated with conc. sulphuric acid, the gas evolved is

Options

A. sulphur dioxide
B. ammonia
C. carbond monoxide
D. carbon dioxide

Explanation

To determine the gas evolved when potassium ferrocyanide crystals are heated with concentrated sulfuric acid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compound**:
Potassium ferrocyanide has the chemical formula \( K_4[Fe(CN)_6] \).

2. **Understand the Reaction**:
When potassium ferrocyanide is heated with concentrated sulfuric acid, it undergoes a decomposition reaction.

3. **Write the Reaction Products**:
The reaction produces several products:
- Potassium sulfate \( K_2SO_4 \)
- Iron(II) sulfate \( FeSO_4 \)
- Ammonium sulfate \( (NH_4)_2SO_4 \)
- Water \( H_2O \)
- Carbon monoxide \( CO \) (the gas evolved)

4. **Identify the Gas**:
Among the products, the gas that is evolved during this reaction is carbon monoxide \( CO \).

5. **Conclusion**:
Therefore, the gas evolved when potassium ferrocyanide is heated with concentrated sulfuric acid is carbon monoxide.

### Final Answer:
The gas evolved is carbon monoxide \( CO \).

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