What term describes a material's ability to resist penetration?

The term that best describes a material's ability to resist penetration is hardness. Hardness refers to the resistance of a material to deformation, particularly permanent deformation, scratching, or penetration. This property is crucial in various applications, especially where protective surfaces are needed to withstand wear and tear, such as in tools, industrial parts, and structures.

Hardness can be measured using different scales, including the Mohs scale, Rockwell hardness test, or Vickers hardness test, depending on the material and context. A hard material can resist being penetrated by another object or force, making it essential in scenarios where durability and longevity are key considerations.

In contrast, ductility refers to a material's ability to deform under tensile stress, elasticity refers to the material's ability to return to its original shape after being stretched or compressed, and toughness describes a material's ability to absorb energy and plastically deform without fracturing. While these properties are important in their own contexts, they do not specifically characterize the resistance to penetration as effectively as hardness does.