What is the color of the outer zone of completion combustion of a candle flame ?

Blue

The correct answer is option 1. Blue.

The color of a flame is determined by the temperature and the chemical elements present in the burning material. In the case of a candle flame, there are typically three zones of color:

1. Inner Zone (Near the Wick):  This is the coolest part of the flame. It appears yellow or orange due to incomplete combustion and the presence of unburned particles, such as soot and carbon.

2. Middle Zone: This zone is hotter than the inner zone but cooler than the outer zone. It usually appears as a bright, yellow color.

3. Outer Zone (Outer Cone): This is the hottest part of the flame, and it appears blue. The blue color is indicative of complete combustion. In this zone, the hydrocarbons in the wax are breaking down into carbon dioxide and water vapor with the release of energy. The blue color is associated with the higher temperature and the presence of excited molecular radicals and ions.

The outer blue zone is often less visible in ambient lighting conditions because the bright yellow color from the middle zone tends to dominate our perception. However, if you observe a candle flame in a dark or dimly lit environment, you may be able to see the distinct blue color at the outer edges of the flame.

In summary, the outer zone of complete combustion in a candle flame appears blue, indicating a high temperature and the efficient burning of hydrocarbons in the wax.