The compound (B) in the below reaction is ,
`C_2H_5Cloverset(KCN)rarrAoverset(H_3O^+)rarrB`

Options

A. ethylene chloride
B. acetic acid
C. propionic acid
D. ethyl cyanide

Explanation

To determine the compound (B) in the reaction sequence given, let's break down the steps involved in the transformation of the starting material (C2H5Cl) through the reactions with KCN and H3O+.

### Step-by-Step Solution:

1. **Identify the Starting Material:**
The starting compound is C2H5Cl, which is ethyl chloride.

2. **Reaction with KCN:**
Ethyl chloride (C2H5Cl) reacts with potassium cyanide (KCN). In this reaction, KCN dissociates into K+ and CN-. The cyanide ion (CN-) acts as a nucleophile and attacks the electrophilic carbon in ethyl chloride. The chlorine atom (Cl) is a good leaving group and is displaced.

**Reaction:**
\[ C_2H_5Cl + KCN \rightarrow C_2H_5CN + KCl \]
Here, we form propionitrile (C2H5CN), which is compound A.

3. **Hydrolysis of the Nitrile:**
The next step involves the hydrolysis of the nitrile (C2H5CN) in the presence of water (H3O+). During hydrolysis, the nitrile group (-CN) is converted into a carboxylic acid (-COOH).

**Reaction:**
\[ C_2H_5CN + H_3O^+ \rightarrow C_2H_5COOH + NH_4^+ \]
This reaction yields propanoic acid (C2H5COOH), which is compound B.

4. **Final Answer:**
Therefore, the compound (B) is propanoic acid (C2H5COOH).

### Conclusion:
The compound (B) in the reaction is propanoic acid.