Why do geologists think earth's core contains mostly iron?

The geologists think that earth's core mostly contain iron because earth has a powerful magnetic field which is because of the molten iron in the core. The constant movement of molten iron in the core causes an electrical current inside the planet which results into the generation of magnetic field which reaches far out into the space. This magnetic field also helps to shield the people living in this planet from the harmful solar radiations.

the correct answer is c.