Deflagration refers to which type of explosion?

• A. A detonation propagating at supersonic speed
• B. A subsonic flame-front explosion
• C. A pressure wave without flame
• D. A purely chemical explosion without flame

Answer: (B)

Deflagration is a flame-front combustion that moves through the unburned mixture at subsonic speeds, driven mainly by heat and mass transfer from the burned gas to the unburned gas. Because it travels slower than the speed of sound, no shock wave accompanies the flame; the propagation is controlled by the flame itself instead of a supersonic pressure front. This makes it distinct from detonation, which is a supersonic, shock-driven process. So the description that fits is a subsonic flame-front explosion. The other options describe phenomena either with a shock wave at supersonic speed, or without a flame, which don’t match deflagration.