What happens when phenol reacts with bromine water followed by NaHSO₃? 

2,4,6-Tribromophenol is produced  

The correct answer is option 3. 2,4,6-Tribromophenol is produced.

When phenol reacts with bromine water, a highly reactive brominating agent, it undergoes electrophilic aromatic substitution. Due to the activating nature of the hydroxyl group (-OH), which directs substitution to the ortho and para positions, phenol reacts readily with bromine to form a tribromo compound. Here is a detailed step-by-step explanation of the reaction:

1. Reaction with Bromine Water:

Phenol reacts with bromine water (Br₂ in water) to form 2,4,6-tribromophenol. The hydroxyl group (-OH) on the benzene ring strongly activates the ortho and para positions, making them highly reactive towards bromination. Bromine water adds to all three positions (two ortho and one para) relative to the hydroxyl group. The reaction can be represented as:

The product is 2,4,6-tribromophenol.

2. Treatment with Sodium Bisulfite (NaHSO₃):

Sodium bisulfite (NaHSO₃) is often used to remove excess bromine from the reaction mixture by reducing bromine (Br₂) to bromide ions (Br⁻). This step does not affect the already formed 2,4,6-tribromophenol. The excess bromine is quenched by NaHSO₃ as follows:

\(\text{Br}_2 + \text{NaHSO}_3 + \text{H}_2\text{O} \rightarrow 2\text{HBr} + \text{NaHSO}_4\)

Thus, after the reaction with bromine water and subsequent treatment with sodium bisulfite, the product formed is: 2,4,6-Tribromophenol is produced