______ combustion is the reason why a candle flame is yellow in colour.

Options

A. Incomplete
B. Complete
C. Rapid
D. Spontaneous

Answer

To solve the question, "______ combustion is the reason why a candle flame is yellow in colour," we need to understand the types of combustion and their characteristics.

### Step-by-Step Solution:

1. **Understanding Combustion**:
- Combustion is a chemical reaction that occurs when a substance reacts with oxygen to produce heat and light. There are two main types of combustion: complete combustion and incomplete combustion.

2. **Identifying Candle Flame Characteristics**:
- A candle flame is typically yellow in color. This color is an important clue that helps us identify the type of combustion occurring.

3. **Complete vs. Incomplete Combustion**:
- **Complete Combustion**: This occurs when there is a sufficient supply of oxygen. In complete combustion, the fuel burns completely, producing carbon dioxide and water. The flame produced is usually blue.
- **Incomplete Combustion**: This occurs when there is a limited supply of oxygen. Incomplete combustion results in the production of carbon monoxide and soot (carbon particles), which gives the flame a yellow color.

4. **Conclusion**:
- Since a candle flame is yellow, it indicates that the combustion occurring is incomplete due to the limited supply of oxygen. Therefore, the answer to the question is "incomplete combustion."

### Final Answer:
**Incomplete combustion is the reason why a candle flame is yellow in colour.**

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