Plasticity: The Property of Material to Retain Deformation Permanently

Plasticity is the property of a material that allows it to retain the deformation it undergoes permanently. When a material is subjected to external forces, it undergoes deformation, which can be either elastic or plastic.

Elastic Deformation:
Elastic deformation occurs when a material is subjected to external forces, and it undergoes temporary deformation. In this case, the material returns to its original shape and size once the forces are removed. The atomic or molecular structure of the material remains unchanged during elastic deformation.

Plastic Deformation:
Plastic deformation occurs when a material is subjected to external forces, and it undergoes permanent deformation. In this case, the material does not return to its original shape and size once the forces are removed. The atomic or molecular structure of the material undergoes rearrangement or dislocation during plastic deformation.

Explanation of Options:
a) Brittleness: Brittleness is the property of a material that causes it to fracture or break when subjected to stress without undergoing significant deformation. Brittle materials do not exhibit plastic deformation and have low ductility and malleability.

b) Ductility: Ductility is the property of a material that enables it to be stretched or drawn into a wire without fracturing. Ductile materials exhibit significant plastic deformation before breaking.

c) Malleability: Malleability is the property of a material that allows it to be hammered or rolled into thin sheets without fracturing. Malleable materials exhibit plastic deformation under compressive forces.

Conclusion:
The correct answer is option 'D' - Plasticity. Plasticity is the property of a material that enables it to retain deformation permanently. Materials exhibiting plasticity can undergo significant plastic deformation before breaking, allowing them to be molded or shaped into various forms.