Correct Answer - A
Case hardening: The process of hardening the surface of wrough iron deposing a surface layer of steel on it is called casehardening is surface layer of steel on it is in called caseheardening and it is done by heating wrought iron in correct with potassium ferrocyanide.
Alternatively, case hardening can also be done by heating wrought iron with charcoal and then plunging it in a suitable oil.