Which of the following substaces on treatment with `P_2O_5` gives ethanenitrile?

Options

A. Propanamide
B. Enthanamide
C. Ethanoic acid
D. N-Methylethyl amine

Explanation

To determine which substance, when treated with P2O5, gives ethanenitrile (C2H5CN), we can analyze each option provided.

### Step-by-Step Solution:

1. **Identify the Structure of Ethanenitrile:**
- Ethanenitrile has the molecular formula C2H5CN. It consists of two carbon atoms, one nitrogen atom, and a functional group (nitrile).

2. **Examine Each Option:**
- **Option A: Propanamide (CH3CH2C(O)NH2)**
- Propanamide, when treated with P2O5, undergoes dehydration. The reaction removes a water molecule (H2O), resulting in the formation of ethanenitrile (C2H5CN).
- Reaction: CH3CH2C(O)NH2 + P2O5 → CH3CH2CN + H2O

- **Option B: Ethanamide (CH3C(O)NH2)**
- Ethanamide, when treated with P2O5, also undergoes dehydration. This reaction will yield ethanenitrile (C2H5CN).
- Reaction: CH3C(O)NH2 + P2O5 → CH3CN + H2O

- **Option C: Ethanoic Acid (CH3COOH)**
- Ethanoic acid reacts with P2O5 to form acetic anhydride (CH3C(O)O) or other products, but it does not directly yield ethanenitrile.
- Reaction: CH3COOH + P2O5 → CH3C(O)O + H2O (not yielding C2H5CN)

- **Option D: N-Methyl Ethylamine (CH3N(CH2CH3)2)**
- N-Methyl ethylamine does not have a carbonyl group or hydroxyl group to react with P2O5, hence it does not undergo any reaction to form ethanenitrile.
- No reaction occurs.

3. **Conclusion:**
- The correct answer is **Option A: Propanamide** and **Option B: Ethanamide** can both yield ethanenitrile upon treatment with P2O5. However, since the question asks for which gives ethanenitrile, the most straightforward answer is **Option B: Ethanamide**.

### Final Answer:
**Ethanamide (Option B) gives ethanenitrile when treated with P2O5.**