Benzene burns with a luminous flame.

Answer

**Step-by-Step Solution:**

1. **Understanding Luminous Flame**:
- A luminous flame is characterized by its bright, glowing appearance. It typically occurs during incomplete combustion of a hydrocarbon fuel, where not all the carbon is converted to carbon dioxide (CO2).

2. **Combustion of Benzene**:
- Benzene (C6H6) is a hydrocarbon composed of 6 carbon atoms and 6 hydrogen atoms. When benzene burns, it can undergo combustion, which can be complete or incomplete.

3. **Complete vs. Incomplete Combustion**:
- In complete combustion, a hydrocarbon reacts with oxygen to produce carbon dioxide and water.
- In incomplete combustion, there is not enough oxygen available, leading to the formation of carbon monoxide (CO) and/or unburned carbon particles (soot).

4. **Why Benzene Produces a Luminous Flame**:
- When benzene burns, if there is insufficient oxygen, some of the carbon atoms do not fully oxidize. This results in the formation of unburned carbon particles or soot.
- These unburned carbon particles emit light when heated, producing a luminous flame.

5. **Conclusion**:
- Therefore, benzene burns with a luminous flame due to the presence of unburned carbon particles resulting from incomplete combustion.

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