The example of an electrophilic substitution reaction is

Options

A.
B.
C. `H_(2)C=CH-CH_(3) underset("peroxide") overset(HBr) to `
`Br_(2)-CH_(2)-CH_(2)-CH_(3)`
D. `H_(2)CCH_(2)-CH_(2)-overset(O)overset(||)(C )-CH_(3)`

Explanation

To determine the example of an electrophilic substitution reaction from the given options, we can analyze each option step by step.

### Step 1: Identify the Reactions
We have four options to consider, and we need to identify which of these represents an electrophilic substitution reaction.

### Step 2: Analyze Each Option
1. **Chlorobenzene with NaOH**:
- This reaction involves the substitution of the chlorine atom in chlorobenzene with a hydroxyl group (OH) to form phenol. This is a nucleophilic substitution reaction, not electrophilic.

2. **Phenol with Diazonium Salt (N2+ and SO3-Na+)**:
- In this case, phenol reacts with a diazonium salt, which acts as an electrophile. The electrophilic substitution occurs where the diazonium ion substitutes for a hydrogen atom on the benzene ring of phenol, leading to the formation of a colored azo compound. This is indeed an electrophilic substitution reaction.

3. **HBA in the presence of peroxide**:
- This reaction follows a radical mechanism and does not involve electrophilic substitution. It typically leads to anti-Markovnikov addition, which is not what we are looking for.

4. **Ketone with Strong Base (LDA)**:
- The reaction of a ketone with a strong base leads to the formation of an enolate ion, which acts as a nucleophile. This is also a nucleophilic substitution reaction, not electrophilic.

### Step 3: Conclusion
From the analysis, the only reaction that qualifies as an electrophilic substitution reaction is the one involving phenol and diazonium salt. Therefore, the correct answer is:

**B. Phenol with Diazonium Salt (N2+ and SO3-Na+)**