Explanation:


The impact strength of a material is an index of its toughness. It is the ability of a material to absorb energy during deformation without fracturing. When a force is applied to a material, it undergoes deformation. The amount of energy required to deform the material depends on its properties such as its structure, composition, and strength. Toughness is an important property for materials that are subjected to impact loads, such as in the case of machine parts or structures.

Impact Strength:


Impact strength is the ability of a material to resist sudden and severe loads. It is the capacity of a material to absorb energy during impact without fracturing. Impact strength is an essential property for materials that are subjected to impact loads. The impact strength of a material is usually measured by the Izod or Charpy impact test.

Toughness:


Toughness is the ability of a material to resist fracture under the action of a sudden and severe load. It is the capacity of a material to absorb energy during deformation without fracturing. Toughness is a crucial property for materials that are subjected to impact loads. Toughness is usually measured by the Charpy or Izod impact test.

Conclusion:


The impact strength of a material is an essential property that determines its resistance to sudden and severe loads. Toughness is an important property that determines the ability of a material to resist fracture under impact loads. The impact strength of a material is an index of its toughness. Therefore, the correct answer is option 'B,' toughness.