Yellow colour in the flame denotes:

Options

A. outermost part
B. middle zone
C. innermost zone
D. none of these

Explanation

To answer the question about what the yellow color in the flame denotes, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Flame Structure**:
- A flame consists of different zones, each with distinct characteristics. The flame can be divided into three main zones: the outermost blue zone, the middle yellow zone, and the innermost black zone.

2. **Identifying the Zones**:
- **Blue Zone**: This is the outermost part of the flame and is known as the non-luminous zone. It indicates complete combustion, which means that the fuel is burning efficiently with enough oxygen.
- **Yellow Zone**: The middle part of the flame is yellow and is referred to as the luminous zone. This zone is where incomplete combustion occurs, leading to the production of soot and the yellow color.
- **Black Zone**: The innermost part of the flame is black and is called the dark zone. This zone is the least hot and also indicates incomplete combustion.

3. **Conclusion**:
- The yellow color in the flame denotes the luminous zone, which is characterized by incomplete combustion. This is where the flame emits light and heat due to the presence of unburned carbon particles.

### Final Answer:
The yellow color in the flame denotes the luminous zone, which is indicative of incomplete combustion.

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