Cyanogen gas is obtained in the reaction

Options

A. `CuSO_(4(aq))+KCN rarr`
B. `K_(4)[Fe(CN)_(6)]overset("heat")rarr`
C. `CH_(3)CN+H_(2)O overset(Delta)rarr`
D. `CH_(3)CONH_(2)+P_(2)O_(5) overset(Delta)rarr`

Explanation

To determine which reaction produces cyanogen gas, let's analyze the given reactions step by step.

### Step 1: Analyze the first reaction
**Reaction:** Copper sulfate (CuSO4) reacts with potassium cyanide (KCN).

**Balanced Equation:**
\[ \text{CuSO}_4 + 4 \text{KCN} \rightarrow 2 \text{CuCN} + K_2SO_4 \]

**Decomposition:**
Copper(I) cyanide (CuCN) is unstable and will decompose:
\[ 2 \text{CuCN} \rightarrow 2 \text{Cu} + \text{C}_2\text{N}_2 \]

**Conclusion:** This reaction produces cyanogen gas (C2N2).

### Step 2: Analyze the second reaction
**Reaction:** Potassium ferrocyanide (K4[Fe(CN)6]) is heated.

**Products:** Heating in concentrated H2SO4 produces carbon monoxide (CO) and in dilute H2SO4 produces hydrogen cyanide (HCN).

**Conclusion:** No cyanogen gas is produced in this reaction.

### Step 3: Analyze the third reaction
**Reaction:** Acetonitrile (CH3CN) is heated with water (H2O).

**Products:** This reaction produces acetic acid (CH3COOH) and ammonia (NH3).

**Conclusion:** No cyanogen gas is produced in this reaction.

### Step 4: Analyze the fourth reaction
**Reaction:** Acetamide (CH3CONH2) reacts with phosphorus pentoxide (P2O5).

**Products:** This reaction leads to the formation of cyanide (CH3C≡N).

**Conclusion:** No cyanogen gas is produced in this reaction.

### Final Conclusion
The only reaction that produces cyanogen gas is the first one, where copper sulfate reacts with potassium cyanide. The cyanogen gas is formed due to the decomposition of copper(I) cyanide.

### Summary of Steps:
1. **First Reaction:** Copper sulfate + KCN → CuCN (unstable) → Cu + Cyanogen gas (C2N2) ✔️
2. **Second Reaction:** K4[Fe(CN)6] + H2SO4 → CO or HCN (no cyanogen) ❌
3. **Third Reaction:** CH3CN + H2O → CH3COOH + NH3 (no cyanogen) ❌
4. **Fourth Reaction:** CH3CONH2 + P2O5 → CH3C≡N (no cyanogen) ❌