What property of a material indicates whether it will burn?

The property of a material that indicates whether it will burn is combustibility. Combustibility refers to the ability of a substance to ignite and support combustion when exposed to an ignition source, such as heat or flame. Materials that are classified as combustible can catch fire and undergo a chemical reaction with oxygen that produces heat, light, and various gases.

Understanding combustibility is critical in firefighting because it helps firefighters determine the risks associated with different materials found at fire scenes. Additionally, knowledge of combustibility allows for the development of mitigation strategies and effective firefighting techniques when dealing with different types of fires.

The other properties listed, including density, thermal expansion, and viscosity, do not inherently dictate a material's ability to burn. Density relates to how compact a substance is, thermal expansion concerns how materials expand when heated, and viscosity refers to a fluid's resistance to flow. While these characteristics may influence how a material behaves in fire situations, they do not determine its flamability or combustibility directly.