Final answer:
Massive stars create iron in their core during the final stages of their lives, leading to their eventual death in a supernova explosion when the fusion of iron consumes energy.
Step-by-step explanation:
The element that massive stars make right before they die is iron. In their final stages, massive stars undergo a series of nuclear fusion reactions, transforming lighter elements into heavier ones. This nucleosynthetic process creates various elements up to iron. When a high-mass star exhausts its nuclear fuel, its interior structure resembles layers of an onion, with different elements fusing in shells around the core. Once iron is produced in the core, the star's end is imminent. The fusion of iron consumes energy instead of releasing it, which means when iron starts to form, the star no longer has a source of outward pressure to counteract gravity, leading to a supernova explosion.