A material's resistance to indentation is included in the mechanical property known as:

The correct answer is hardness, which refers to a material's resistance to indentation, scratching, or abrasion. Hardness is a critical mechanical property that helps determine how well a material can withstand wear and maintain its integrity under stress.

In practical applications, hardness is often quantified through various tests, such as the Rockwell, Brinell, or Vickers tests, which assess how deep an indentor penetrates the material under a specific load. Materials that exhibit high hardness are typically better suited for applications where surface wear and deformation are concerns, such as in cutting tools or structural components exposed to abrasive environments.

Toughness relates to a material’s ability to absorb energy and deform plastically before fracturing, which is not directly related to its resistance to indentation. Brittleness refers to a material's tendency to fracture or snap without significant deformation when subjected to stress, while elasticity measures how well a material returns to its original shape after being deformed. Both toughness and brittleness focus more on how a material reacts to stress than on its hardness. Elasticity specifically pertains to reversible deformation and is not associated with resistance to surface indentation.