Which of the following reaction is correct :

Options

A. `(1)` `CH_(3)CH_(2)-Br+KCNtoCH_(3)CH_(2)-NC`
B. `(2)` `CH_(3)CH_(2)-Br+AgCNtoCH_(3)CH_(2)-CN`
C. `(3)` `CH_(3)CH_(2)-Br+KNO_(2)toCH_(3)CH_(2)-NO_(2)`
D. `(4)` `CH_(3)CH_(2)-Br+AgNO_(2)toCH_(3)CH_(2)-NO_(2)`

Answer

To determine which of the given reactions is correct, we will analyze each reaction step by step.

### Step 1: Analyze Reaction 1
- **Reaction**: CH3CH2Br + KCN
- **Mechanism**: KCN dissociates into K⁺ and CN⁻. The CN⁻ acts as a nucleophile and attacks the carbon atom bonded to Br, leading to substitution.
- **Product**: CH3CH2CN + KBr

### Step 2: Analyze Reaction 2
- **Reaction**: CH3CH2Br + AgCN
- **Mechanism**: AgCN dissociates into Ag⁺ and CN⁻. The CN⁻ attacks the carbon atom bonded to Br, replacing it.
- **Product**: CH3CH2NC + AgBr (isocyanide is formed)

### Step 3: Analyze Reaction 3
- **Reaction**: CH3CH2Br + KNO2
- **Mechanism**: KNO2 dissociates into K⁺ and NO2⁻. The NO2⁻ attacks the carbon atom bonded to Br, leading to substitution.
- **Product**: CH3CH2ONO + KBr

### Step 4: Analyze Reaction 4
- **Reaction**: CH3CH2Br + AgNO2
- **Mechanism**: AgNO2 dissociates into Ag⁺ and NO2⁻. The NO2⁻ attacks the carbon atom bonded to Br, replacing it.
- **Product**: CH3CH2NO2 + AgBr

### Conclusion
After analyzing all four reactions, we find that:
- Reaction 1 produces a nitrile (correct).
- Reaction 2 produces an isocyanide (correct).
- Reaction 3 produces an alkyl nitrite (correct).
- Reaction 4 produces an alkyl nitro compound (correct).

However, the question asks for the "correct" reaction, which typically refers to the one that produces a stable and commonly accepted product. In this context, **Reaction 4 (CH3CH2Br + AgNO2 → CH3CH2NO2 + AgBr)** is the most straightforward and commonly recognized reaction, making it the correct answer.

### Final Answer
**The correct reaction is Reaction 4: CH3CH2Br + AgNO2 → CH3CH2NO2 + AgBr.**