Which property measures a material's ability to return to its original shape after deformation?

The property that measures a material's ability to return to its original shape after deformation is elasticity. Elasticity is defined as the capacity of a material to deform under stress and then return to its original dimensions once the stress is removed. This characteristic is vital in many materials, particularly in rubber and metals, as it allows structures and components to absorb and dissipate energy without undergoing permanent changes.

In contrast, tensile strength refers to the maximum amount of tensile (stretching) stress a material can withstand before failing, but it does not directly relate to the ability to return to shape after deformation. Plasticity describes a material's ability to undergo permanent deformation without breaking, meaning it will not return to its original shape once the stress is removed. Viscosity is a measure of a fluid's resistance to flow, which is unrelated to deformation and shape retention in solid materials. Thus, elasticity is the correct choice when discussing a material’s capacity to revert to its original form after experiencing stress.