The correct option is C Magnetite
Magnetite is a type of iron ore which has a very high content of iron, almost up to 70 per cent. And the amount of iron it has makes it one of the finest iron ore with exceptional magnetic properties. That is why this type of iron is extensively sought out in the electrical industry. As compared to Magnetite, Hematite has a slightly lower content of iron, around 56-60%. Almost all industries use Hematite even though it contains a lower amount of iron content as compared to Magnetite; Hematite is abundantly available. Hence Hematite is also known by the name, industrial iron.
So Hema would craft the sword from Magnetite for the king, as per his need for a magnetic sword.