Which of the following is considered a physical hazard?

A physical hazard refers to any substance or situation that can cause harm or injury due to its physical properties. Flammable liquids are classified as a physical hazard because they have the potential to ignite and cause fires or explosions when exposed to an ignition source. Understanding the nature of flammable liquids in a laboratory setting is crucial for ensuring proper safety measures are in place, such as appropriate storage and handling practices.

The other options, while related to safety and materials used in laboratories, do not represent physical hazards. Non-hazardous waste generally does not pose a risk of physical harm, stable compounds are characterized by their lack of reactive or hazardous behaviors under normal conditions, and eco-friendly materials are designed to minimize environmental impact without being inherently dangerous in a physical sense. Thus, the identification of flammable liquids as a physical hazard is essential for promoting safety and reducing the risk of incidents in laboratory environments.