What element accumulates in the inert core of a massive star just before a catastrophic collapse?

Answer

Iron

The final pre-supernova burning phase, silicon burning, produces iron ($ ext{Fe}$) and nickel ($ ext{Ni}$), leading to an inert iron core at the very center where fusion ceases.

What element accumulates in the inert core of a massive star just before a catastrophic collapse?
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