What characteristic makes a material classified as flammable?

Answer: B — It has a flash point below 100°F (37.8°C)

A material is classified as flammable primarily based on its flash point, which is the lowest temperature at which it can vaporize to form an ignitable mixture in air. When a substance has a flash point below 100°F (37.8°C), it is deemed flammable because it can easily produce sufficient vapors to ignite at relatively low temperatures. This characteristic is crucial for assessing risks in handling, storing, and responding to incidents involving such materials. In contrast, being solid at room temperature does not necessarily indicate flammability, as many solids can remain non-flammable regardless of their state. Likewise, a material being non-reactive with air typically points to stability rather than flammability; it might not ignite easily. Additionally, the suitability of containment materials, such as plastic containers, does not inherently relate to whether a material is flammable; many flammable substances can indeed be stored safely in plastic if appropriate precautions are followed. Thus, the defining feature for flammability is specifically the flash point.