Which of the following statement is incorrect ?

Options

A. `C_(2)H_(5)Br` reacts with alc. KOH to form `C_2H_4`
B. `C_2H_5Br` when treated with metallic sodium gives ethane
C. `C_2H_5Br` when treated with sodium ethoxide forms diethyl ether
D. `C_(2)H_(5)Br` with AgCN forms ethyl isocyanide

Answer

To solve the question, we need to analyze each statement regarding the reactions of ethyl bromide (C2H5Br) and determine which one is incorrect.

### Step-by-Step Solution:

1. **Statement 1**: When C2H5Br reacts with alcoholic KOH, it forms ethene (C2H4).
- **Reaction**: C2H5Br + KOH (alcoholic) → C2H4 + KBr + H2O
- **Analysis**: This reaction is a dehydrohalogenation reaction, which is correct. Thus, this statement is correct.

2. **Statement 2**: Ethyl bromide when treated with metallic sodium gives ethane.
- **Reaction**: 2 C2H5Br + 2 Na → C4H10 + 2 NaBr
- **Analysis**: This is a Wurtz reaction, and the product is butane (C4H10), not ethane (C2H6). Therefore, this statement is incorrect.

3. **Statement 3**: C2H5Br when treated with sodium ethoxide forms diethyl ether.
- **Reaction**: C2H5Br + C2H5ONa → C2H5OC2H5 + NaBr
- **Analysis**: This is a reaction to form diethyl ether, which is correct. Thus, this statement is correct.

4. **Statement 4**: When C2H5Br reacts with AgCN, it forms ethyl isocyanide.
- **Reaction**: C2H5Br + AgCN → C2H5CN + AgBr
- **Analysis**: The product formed is ethyl cyanide (not isocyanide). Thus, this statement is also incorrect.

### Conclusion:
- The incorrect statements are **Statement 2** (it produces butane, not ethane) and **Statement 4** (it produces ethyl cyanide, not ethyl isocyanide). However, since the question asks for one incorrect statement, the most straightforward answer is **Statement 2**.

### Final Answer:
**Option 2 is the correct answer as it is the incorrect statement.**