Coupling of benzene diazonium chloride with `1-`naphthol in alkaline medium will give:

Explanation

To solve the problem of what product is formed when benzene diazonium chloride couples with 1-naphthol in an alkaline medium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The first reactant is **benzene diazonium chloride** (C6H5N2Cl).
- The second reactant is **1-naphthol** (C10H8O), which has a hydroxyl (–OH) group attached to the first carbon of the naphthalene ring.

2. **Draw the Structure of 1-Naphthol**:
- The structure of 1-naphthol consists of a naphthalene ring with a hydroxyl group at the 1-position.
- The structure can be represented as follows:
```
OH
|
/ \
| |
| |
\ /
|
C
```

3. **Alkaline Medium**:
- In an alkaline medium, the hydroxyl group (–OH) can lose a proton (H+) to form a phenoxide ion (C10H7O⁻), which is more nucleophilic.

4. **Formation of Phenoxide Ion**:
- The reaction in the alkaline medium leads to the formation of the phenoxide ion:
```
C10H8O + OH⁻ → C10H7O⁻ + H2O
```

5. **Nucleophilic Attack**:
- The phenoxide ion (C10H7O⁻) will act as a nucleophile and attack the electrophilic nitrogen of the benzene diazonium chloride.
- The reaction can be represented as:
```
C6H5N2⁺Cl⁻ + C10H7O⁻ → C6H5N2C10H7O + Cl⁻
```

6. **Formation of the Coupling Product**:
- The product formed will be a coupling product where the diazonium group is attached to the naphthol. The structure can be represented as:
```
O
||
C6H5-N=N-C10H7
```

7. **Final Product**:
- After the reaction, the product is a compound known as **1-(phenylazo)naphthol**, which can be represented as:
```
C6H5-N=N-C10H7OH
```

### Final Answer:
The coupling of benzene diazonium chloride with 1-naphthol in alkaline medium will give **1-(phenylazo)naphthol**.