The three zones of a candle flame are the dark zone, the luminous zone, and the outermost zone. Each zone represents a different stage of the combustion process and has distinct characteristics.

1. Dark Zone:
The dark zone is the innermost part of the flame, located just above the wick. It is called the dark zone because it appears dark or black due to incomplete combustion. The key features of this zone include:

- Lack of oxygen: In this zone, there is insufficient oxygen for complete combustion, resulting in the production of soot and unburned carbon particles.
- High temperature: The dark zone has the highest temperature in the flame, reaching up to 1400°C (2552°F). The intense heat vaporizes the fuel, enabling it to rise to the next zone.
- No visible light: As the combustion is incomplete, the dark zone does not emit visible light, making it appear dark compared to the other zones.

2. Luminous Zone:
The luminous zone is the middle part of the flame and is characterized by its yellowish color and visible light emission. This zone has the following characteristics:

- Sufficient oxygen: As the fuel rises from the dark zone, it encounters sufficient oxygen from the surrounding air, leading to more complete combustion.
- Lower temperature: The temperature in the luminous zone is relatively lower than the dark zone, ranging from 800°C to 1200°C (1472°F to 2192°F). The lower temperature results in the formation of glowing particles, which emit visible light.
- Presence of glowing particles: The luminous zone contains tiny carbon particles that are heated to incandescence, giving the flame its yellowish glow.

3. Outermost Zone:
The outermost zone of the candle flame is the faint blue outer cone. This zone has the following characteristics:

- Abundant oxygen: The fuel in this zone has access to sufficient oxygen from the surrounding air, allowing for complete combustion.
- Lower temperature: The outermost zone has the lowest temperature in the flame, typically around 300°C to 500°C (572°F to 932°F).
- Almost invisible: The flame in this zone emits very little light and appears almost invisible to the naked eye. The blue color is due to the emission of radiation at shorter wavelengths.

Overall, the three zones of a candle flame represent different stages of the combustion process, with the dark zone being the hottest but least efficient in terms of complete combustion, the luminous zone emitting visible light due to incandescent carbon particles, and the outermost zone having the lowest temperature and emitting minimal light.

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