How is the hardness of a metal best described?

The hardness of a metal is best described as the resistance to plastic deformation due to indentation. This characteristic is crucial because it directly reflects how well a material can withstand mechanical forces without undergoing permanent changes in shape. When a hard material is subjected to an indenting force, it will deform less than a softer material would under the same conditions, making it an important factor in applications where wear resistance is critical.

Hardness is typically measured using various scales, such as the Rockwell, Brinell, or Vickers tests, which essentially evaluate how much a material resists deformation from an indenter. This property is significant not only in manufacturing processes but also in determining the longevity and durability of components in various industries.

While environmental corrosion resistance, electrical conductivity, and relative density are valuable properties of metals, they do not directly define hardness. Hence, the correct description centers on resistance to indentation and associated plastic deformation.