What type of explosion occurs at a speed less than that of sound?

The correct choice is deflagration, which refers to a type of explosion that propagates at a speed less than that of sound. This slower rate of combustion allows for the pressure wave generated by the explosion to move through the material more gently, creating a less violent release of energy compared to other types of explosions.

Deflagration typically occurs in combustible materials where the reaction travels through the unburnt material at subsonic speeds, resulting in a burning front that moves through the fuel. This type of explosion is commonly observed in many fires and situations involving flammable gases and volatile liquids, where the combustion reaction is more controlled and occurs over time, unlike faster reactions.

In contrast, detonation involves a rapid transformation of chemical energy into thermal energy that produces shock waves traveling at supersonic speeds, resulting in a significantly more violent explosion. An implosion describes a structural failure that occurs inwardly, usually involving a sudden collapse of a structure due to external pressure, rather than a combustion reaction. Combustion, while related to the process of burning, is a more general term that does not specifically refer to the rapidity of the reaction or the type of explosion. Thus, deflagration is the most accurate term that describes an explosion occurring