The hardness of a material is least influenced by
- AGrain size of the material.
- BType of heat treatment performed.
- CAmount of alloying elements present.
- DDensity of the material.Correct
Solution
Concept
Hardness depends on microstructure and composition, not on density.
Step-by-step solution
1. Hardness means resistance to indentation or scratching. 2. Smaller grain size gives higher hardness (Hall-Petch effect). 3. Heat treatment (quenching, tempering) changes microstructure and hardness. 4. Alloying elements (carbon, chromium etc.) change hardness a lot. 5. Density is only mass per unit volume and has no direct link with hardness. 6. So density is the least influencing factor.
Explanation
Hardness is controlled by grain size, heat treatment and alloying. Density is a physical property and does not directly control hardness. So option D is the answer.
Why the other options are wrong
A: finer grains increase hardness. B: heat treatment changes microstructure. C: alloying elements strengthen and harden the metal.
Shortcut
Hardness depends on microstructure and composition, not on density.
Common mistake
Thinking a denser material is always harder (for example lead is dense but soft).
Correct answer: D) Density of the material.