The right answer is A. Hardness.
The hardness of a material defines the resistance of a surface of the sample to the penetration of a punch, for example a hardened steel ball (Brinell hardness) or a diamond pyramid (Vickers hardness). If it resists well, it is said hard, otherwise it is soft. The hardness is measured on different scales depending on the type of material considered.
Unlike minerals whose hardness is characterized by scratching (Mohs scale), bounce or penetration tests are usually used to characterize the hardness of metals, plastics and elastomers. These tests have the advantage of being simpler to perform and give reproducible results. There is a wide variety of possible hardness tests, they are widely used in quality control to compare or estimate the strength or stiffness of materials.
