Q.State the names of the hardest material and the softest material.

Hardness, strength and toughness are three related but genuinely independent mechanical properties of a material, and it is easy to mix them up. Hardness is a material's resistance to plastic (permanent) deformation, and, more loosely, to scratching, abrasion, cutting or bending — diamond is the hardest common material, aluminium a notably soft metal. Strength is a measure of how large a deforming force is needed to produce deformation at all — a stronger material (like steel) needs a larger force to deform than a weaker one (like plasticine clay). Toughness is a material's ability to resist actually fracturing (breaking apart) when a force is applied — plasticine clay, though weak, is relatively tough because it can be stretched and reshaped extensively without breaking. …