What defines a flame?

A flame is defined as a body of gaseous material involved in combustion. This definition encompasses the characteristics of a flame, which is the visible, luminous part of a fire. It occurs when a fuel combusts in the presence of an oxidizer, typically oxygen, producing heat and light.

Flames consist primarily of gases that are a byproduct of the combustion process, including hot gases and particles that are produced when solid or liquid fuels undergo exothermic reactions with oxygen. The presence of energy in the form of heat causes the gases to glow, resulting in the visible aspect of the flame. Understanding this essential concept is crucial in fire investigations, as identifying the characteristics and behavior of flames can aid in determining the fire's source and progression.

The other options do not accurately portray the nature of a flame, which is fundamentally a gaseous phenomenon rather than a solid, liquid, or spark.