On heating `K_4[Fe(CN)_6]` with conc. `H_2SO_4` gives the gas

Options

A. `SO_2`
B. `CO_2`
C. `CO`
D. `NO_2`

Explanation

To solve the problem of what gas is released when heating \( K_4[Fe(CN)_6] \) with concentrated \( H_2SO_4 \), we can follow these steps:

### Step 1: Understand the Reactants
We start with potassium ferrocyanide, \( K_4[Fe(CN)_6] \), which is a coordination compound containing iron and cyanide ions. When heated with concentrated sulfuric acid, a reaction occurs.

### Step 2: Write the Reaction
When \( K_4[Fe(CN)_6] \) is heated with concentrated \( H_2SO_4 \), it decomposes. The general reaction can be represented as:
\[ K_4[Fe(CN)_6] + H_2SO_4 \rightarrow \text{Products} \]

### Step 3: Identify the Products
The products of this reaction include:
- Potassium sulfate (\( K_2SO_4 \))
- Iron(II) sulfate (\( FeSO_4 \))
- Ammonium sulfate (\( (NH_4)_2SO_4 \))
- Carbon monoxide gas (\( CO \))

### Step 4: Determine the Gas Released
From the products formed, we can see that the gas released during the reaction is carbon monoxide (\( CO \)).

### Step 5: Conclusion
Thus, the gas released when heating \( K_4[Fe(CN)_6] \) with concentrated \( H_2SO_4 \) is carbon monoxide (\( CO \)).

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

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