Which class is indicated by a yellow or yellow/red placard?

The correct choice designates Class 5 materials, which are oxidizers and organic peroxides. The yellow or yellow/red placard is specifically used to signal the presence of these hazardous materials. They are categorized as substances that can cause or enhance the combustion of other materials, and they require careful handling and storage to prevent fires or explosions. This distinctive yellow or yellow/red color of the placard helps emergency responders quickly identify the nature of the hazard when arriving at an incident scene, ensuring appropriate safety measures can be enacted. Understanding the color coding and placard system is crucial for effective hazard communication and response.