Final answer:
Plasticity is the mechanical property of a metal that enables it to deform permanently without breaking or rupturing.
Step-by-step explanation:
The mechanical property of a metal that allows it to deform permanently without breaking or rupturing is called plasticity.
When a material exhibits plastic behavior, it means it can undergo irreversible deformation and does not return to its original shape and size, even after the load is removed. This property is especially prominent in ductile materials like metals, which show a gradual decrease in stress as they approach the breaking point.