Final answer:
A flame going out unexpectedly and creating a popping sound is known as a backfire or a flashback.
Step-by-step explanation:
This occurs when there is a sudden combustion of unburned fuel in the combustion chamber or in the fuel delivery system of a burner or a flame torch. It can happen due to various reasons such as insufficient air supply, incorrect fuel-air mixture ratio, or a buildup of flammable gases.
For example, in a candle, if the wick is not properly trimmed or there is not enough oxygen supply, the flame may receive an excess amount of fuel and the unburned fuel can accumulate in the combustion chamber. When the flame goes out and then comes into contact with the accumulated fuel, it can cause a small explosion or popping sound.
To prevent backfires or flashbacks, it is important to ensure proper ventilation, maintain the correct fuel-air mixture, and regularly maintain and clean the combustion equipment. Therefore when a flame goes out unexpectedly and creates a popping sound, it is known as a backfire or a flashback.