What is the flash point of a substance?

The flash point of a substance is defined as the temperature at which it can vaporize enough to form an ignitable mixture with air. This characteristic is critical because it indicates the potential flammability of a material. When a substance reaches its flash point, it produces vapor that can ignite if an appropriate ignition source is present. Understanding the flash point is vital for safe handling, storage, and transportation of combustible materials, as it helps in determining the risks involved and implementing appropriate safety measures.

In contrast, the other choices do not accurately represent the definition of a flash point. Condensation of gas molecules pertains to a different physical state change, solidification is related to the freezing point, and the temperature below which a substance cannot be transported does not describe flammability but rather regulatory criteria for safe transport. Thus, option B stands out as the accurate definition of flash point.