How is a combustible liquid typically identified?

A combustible liquid is typically identified by its closed-cup flash point being at or above 100°F. This temperature indicates the lowest point at which the liquid can vaporize to form an ignitable mixture with air. Understanding flash points is crucial in laboratory settings because it directly impacts the handling and storage of flammable materials. Materials with a flash point in this range can easily ignite if proper precautions are not taken, making awareness of this property essential for safety protocols.

The other options, while they may describe certain characteristics of liquids, do not provide a reliable or standard method for identifying combustible liquids. Vivid coloration, strong odor, and viscosity are not definitive indicators of a liquid's combustibility. For instance, a clear liquid may still have a high flash point, and not all combustible liquids emit strong odors. Therefore, establishing identification based on flash points is a standardized and safety-centric approach.