The element involved in making human blood red is which of the following?

The story behind the answer

Iron is the key element in hemoglobin, the protein that carries oxygen in red blood cells. Each hemoglobin molecule contains heme groups with an iron atom at the center; when iron binds oxygen, it changes the way light is absorbed and reflected, giving oxygenated blood its bright red color (and a darker red when deoxygenated).

Fun context: Not all creatures use iron. Many mollusks and some arthropods use copper-based hemocyanin, which turns their blood blue when oxygenated. Cobalt isn’t used to carry oxygen but is in vitamin B12, essential for making red blood cells. Memory tip: Iron (chemical symbol Fe) makes both rust and blood appear reddish—think “Fe = ferrum = ferrous = red.”