The correct answer is option 'B' - three.

The Zones of a Flame

A flame is a visible indication of the process of combustion. It consists of different zones, each with distinct characteristics. The three zones of a flame are:

1. Innermost Zone (Dark Zone)
This is the innermost and darkest part of the flame. It is also known as the zone of complete combustion. It appears dark because the fuel is completely consumed in this zone and there is no unburnt fuel left. The temperature in this zone is very high.

2. Middle Zone (Yellow Zone)
The middle zone is also known as the luminous zone. It appears yellow due to the presence of partially burnt fuel particles. The temperature in this zone is lower than the innermost zone but higher than the outermost zone.

3. Outermost Zone (Blue Zone)
The outermost zone is also known as the non-luminous zone. It appears blue because the fuel particles in this zone have not yet ignited. The temperature in this zone is the lowest among the three zones.

Explanation of the Answer

The correct answer is option 'B' because there are three zones of a flame. The innermost zone is the dark zone, followed by the middle zone which is the yellow zone, and finally the outermost zone which is the blue zone. These zones have different characteristics and temperatures, indicating the varying stages of combustion.

It is important to understand the zones of a flame as they provide valuable information about the efficiency of combustion and the presence of unburnt fuel. By observing the colors and characteristics of a flame, one can determine if the combustion process is complete or if there is a need for adjustments in the fuel-air mixture.

In conclusion, the three zones of a flame are the innermost dark zone, the middle yellow zone, and the outermost blue zone. Each zone plays a crucial role in the combustion process and provides valuable insights into the efficiency of combustion.

It is because there are only three zones in a flame i.e. dark zone, non luminous zone, luminous zone