Benzonitrile on reaction with `C_2 H_5 MgBr`, followed by hydrolysis, gives.

Options

A.
B.
C.
D.

Explanation

To solve the problem of what product is formed when benzonitrile reacts with ethyl magnesium bromide followed by hydrolysis, we can break it down into several steps:

### Step 1: Identify the Reactants
The reactants in this reaction are:
- Benzonitrile (C6H5CN)
- Ethyl magnesium bromide (C2H5MgBr)

### Step 2: Understand the Reaction Mechanism
Benzonitrile contains a cyano group (–C≡N) which is polarized due to the electronegativity of nitrogen. The carbon atom in the cyano group is electrophilic, making it susceptible to nucleophilic attack.

### Step 3: Nucleophilic Attack
The ethyl group (C2H5–) from ethyl magnesium bromide acts as a nucleophile. It attacks the electrophilic carbon of the cyano group in benzonitrile. The reaction can be represented as follows:

\[ \text{C}_6\text{H}_5\text{C} \equiv \text{N} + \text{C}_2\text{H}_5\text{MgBr} \rightarrow \text{C}_6\text{H}_5\text{C}(\text{C}_2\text{H}_5)\text{N} \text{MgBr} \]

### Step 4: Formation of the Intermediate
The product of this nucleophilic attack is an intermediate compound where the cyano group is now attached to the ethyl group, forming a compound with a carbon-nitrogen bond and a magnesium bromide ion:

\[ \text{C}_6\text{H}_5\text{C}(\text{C}_2\text{H}_5)\text{N} \text{MgBr} \]

### Step 5: Hydrolysis of the Intermediate
Upon hydrolysis, the intermediate reacts with water. The magnesium bromide part is removed, and the cyano group is converted to a carbonyl group (–C=O), resulting in the formation of an imine which then hydrolyzes to form a ketone.

The final product after hydrolysis is:
\[ \text{C}_6\text{H}_5\text{C}(\text{C}_2\text{H}_5)=\text{O} \]

This compound is **ethyl phenyl ketone**, also known as **acetophenone**.

### Conclusion
Thus, the final product formed when benzonitrile reacts with ethyl magnesium bromide followed by hydrolysis is **acetophenone (C6H5C(O)C2H5)**.