Brittleness
Brittleness is a property of material which breaks with little or no deformation.

Toughness: When a huge external force is applied on a metal, the metal will experience fracture. Toughness is the ability of a metal to resist fracture. The ability of a material to resist fracture due to high impact loads, is called toughness.

Hardness: Hardness is the ability of a metal to resist permanent change of shape caused by an external force.