Amongst the compounds given, the one that would form a brilliant colored dye on treatment with `NaNO_2` in dil. `HCl` followed by addition to an alkaline solution of `beta-`naphthol is

Options

A.
B.
C.
D.

Answer

To solve the question, we need to determine which compound can undergo diazotization with sodium nitrite (NaNO2) in dilute hydrochloric acid (HCl) and subsequently react with beta-naphthol to form a colored dye.

### Step-by-Step Solution:

1. **Identify the Reaction Type**:
The reaction involves diazotization, which is the process of converting an amine (specifically an aromatic amine) into a diazonium salt using NaNO2 and HCl. This occurs at low temperatures (0°C to 5°C).

2. **Recognize the Required Functional Group**:
For diazotization to occur, the compound must contain an amino group (-NH2) attached to an aromatic ring. This is crucial because only aromatic amines can form diazonium salts.

3. **Form the Diazotization Product**:
When the aromatic amine is treated with NaNO2 and HCl, it forms a diazonium salt. The general structure of the diazonium salt formed from an aromatic amine can be represented as Ar-N2^+Cl^-, where Ar is the aromatic part of the amine.

4. **Coupling with Beta-Naphthol**:
The diazonium salt can then react with beta-naphthol in an alkaline medium. The reaction involves a coupling process where the diazonium group (N2^+) replaces a hydrogen atom on the beta-naphthol, leading to the formation of a colored azo dye.

5. **Select the Correct Compound**:
Among the given compounds, identify the one that contains an aromatic amine structure. This compound will be the only one capable of undergoing the described reactions to form the colored dye.

6. **Final Product**:
The final product will be an azo dye, which is characterized by the presence of the azo group (-N=N-) linking the two aromatic systems (the original aromatic amine and beta-naphthol).

### Conclusion:
The compound that would form a brilliant colored dye upon treatment with NaNO2 in dilute HCl followed by reaction with beta-naphthol is the one that contains an aromatic amine group.