Plasticity is defined as
A.Ability to regain its original shape.
B.Ability to flow when subjected to stress.
C.Ability to change shape permanently
D.Both b and c.

Hint: Plasticity, from the name itself we can depict its meaning that it is the property related to the changing of shape when stress is applied on it.

Complete step by step answer:
Plasticity is the property of the substance or a body that tells about the ability of certain solids to flow or to change shape permanently when they are subjected to some kind of stress of some magnitude Some substances experience temporary deformation, or elastic behavior, and some of those experience failure of the material, or rupture.
When a solid or a substance undergoes some type of stress the action of external forces, plasticity enables the solid to undergo permanent deformation without rupture (sometime rupture or fracture).
Sometimes it causes fracture or rupture of material. It causes plastic deformation which basically occurs in the metal forming process which includes rolling, pressing, forging and wire drawing etc.
We will understand plasticity by taking an example, a solid part of a metal being bent or pounded into a new shape exhibits plasticity as stable changes occur within the material itself.

Therefore, option D is correct.

Note: Plasticity in a crystal of pure metal is primarily caused by the two modes of deformation in the crystal lattice which are slipping and twinning. Plasticity of a substance is directly proportional to the malleability and ductility of the material.