Which term defines the property that enables a material to resist plastic deformation, penetration, indentation, and scratching?

• A. Elasticity
• B. Ductility
• C. Hardness
• D. Conductivity

Answer: (C)

Hardness is the property that defines a material’s resistance to surface deformation, including plastic deformation, penetration, indentation, and scratching. It’s measured by how well a material resists leaving an impression or being scratched when a harder object is pressed or drawn across its surface. This trait is closely linked to wear resistance, since surfaces that are harder tend to resist scratching and wear better in service.

Elasticity, by contrast, is about recovering shape after small deformations and does not address resistance to indentation or scratching. Ductility describes how much plastic deformation a material can undergo before failure, not how hard its surface is. Conductivity is about how well a material conducts heat or electricity, not surface deformation resistance.

So, the term that best fits resisting plastic deformation, penetration, indentation, and scratching is hardness. Diamond’s extreme hardness exemplifies this concept, while lead’s softness illustrates a low hardness.