Correct Option
The correct option isPartial combustion and yellow colour.
Explanation
A candle flame is divided into three distinct zones based on the availability of oxygen and the degree of combustion: the outer zone (non-luminous), the middle zone (luminous), and the inner zone (dark). These zones vary in colour, temperature, and combustion efficiency.
Detailed Analysis
- Luminous Zone (Middle Zone): This zone is characterized by a limited supply of oxygen, leading to partial combustion of the wax vapours. The unburnt carbon particles produced in this region get heated up and glow, emitting a yellow light. It is moderately hot.
- Non-Luminous Zone (Outer Zone): This is the zone of complete combustion due to an ample supply of oxygen. It burns with a blue flame and has the highest temperature (maximum heat).
- Dark Zone (Inner Zone): This is the area around the wick containing unburnt wax vapours. No combustion takes place here due to a lack of oxygen, making it appear black. It is the least hot region of the flame.
Therefore, the luminous zone is defined by partial combustion and a yellow colour.
Key Takeaway
The Luminous Zone is the middle region of a candle flame where partial combustion occurs due to insufficient oxygen, resulting in a yellow flame caused by glowing carbon particles.