Which hazard class is indicated by a placard for radioactive materials?

The choice indicating radioactive materials is correct because the placard system used for hazardous materials, including those regulated by the Department of Transportation (DOT), employs specific colors and symbols to communicate the nature of the hazard. Radioactive materials are categorized under a particular placard featuring a trefoil symbol, which is distinctive and universally recognizable as indicating radiation hazards. This visual cue alerts responders and those handling or encountering the materials about the potential dangers associated with radiation exposure.

The other options consist of classes of hazards that have their own specific placards but do not represent radioactive materials. Explosives, for example, are marked with a different symbol that indicates the potential for detonation. Corrosive materials are identified by placards that highlight their ability to corrode or damage living tissue and materials. Flammable substances are indicated with a flame symbol, warning of fire hazards. Thus, each hazard class has its unique identifier and corresponding placard, making the choice of “radioactive” the only correct representation of that specific hazard class.