Question

What makes the middle zone of candel flame visible?​

Answer 1

Answer:

The incomplete burning of wax vapour produces carbon particles and carbon monoxide. The unbrunt carbon particles becomes hot and emit yellow light. It is the glow of hot carbon particles which makes the middle zone of a flame luminous.

Answer 2

Answer:

$\bf\green{✿}\red{Answer}$

The innermost zone, directly above the wick, contain wax that has been vaporized but that is unburnt. It is the darkest zone. The middle zone is yellow and luminous because As it is an oxygen-depleted zone, insufficient oxygen exists to burn all of the wax vapor. As such, partial combustion of wax takes place.