Which property of a material does NOT describe its behavior under load?

The property of a material that does not describe its behavior under load is mass. Mass refers to the quantity of matter in a material and does not influence how the material behaves when subjected to external forces.

In contrast, brittleness, elasticity, and ductility are all properties that provide insights into how a material responds to applied stress or load. Brittleness describes a material's tendency to break or shatter under stress without significant deformation. Elasticity refers to the ability of a material to return to its original shape after the load is removed, which is crucial in understanding how materials deform under various conditions. Ductility indicates the extent to which a material can be stretched or deformed before it breaks, which is essential in applications where materials are subjected to tensile forces.

Understanding these properties allows engineers to select appropriate materials for specific applications based on their expected performance under load. Mass, while important for other considerations such as weight and density, does not provide relevant information regarding mechanical behavior under stress.