When explosives detonate, which event causes the creation of a shock wave?

The correct answer highlights the concept of the blast pressure effect. When explosives detonate, a rapid chemical reaction occurs, producing a large volume of gas in a very short period. This intense and sudden release of gas generates an extremely high pressure in the surrounding area. As this pressure wave propagates outward from the point of detonation, it creates a shock wave that travels through the air, resulting in what we experience as the blast wave associated with an explosion. The shock wave is characterized by a rapid increase in pressure followed by a sudden drop, creating a wavefront that can cause significant destruction to nearby structures and objects.

Contextually, while the rapid expansion of gases is indeed a crucial part of the process, it is the resultant blast pressure effect that primarily describes how the shock wave is formed. The ignition of solid materials pertains more to the initial phase of an explosion but does not directly create the shock wave. The decay of unstable compounds is related to the characteristics of certain types of explosives but is not directly responsible for the shock wave production associated with detonations. Therefore, focusing on the blast pressure effect is key to understanding the mechanics of how shock waves are generated in explosive events.