Final answer:
Liquified acetylene is categorized as a reactive flammable material due to its propensity to burn readily and its dangerous reactivity in air that can lead to spontaneous ignition.
Step-by-step explanation:
Liquefied acetylene is a reactive flammable material. Acetylene belongs to the group of alkynes that are known for burning readily, which makes them excellent for applications such as welding and cutting metals using an acetylene torch. This torch exploits the high heat of combustion of acetylene.
While acetylene itself is a volatile, waxy, white solid, it is dangerously reactive in air, capable of glowing with white light and spontaneously igniting. Given its flammability and the potential for violent reaction, acetylene can be considered a dangerously reactive and flammable material, which corresponds to option B).