What percentage of a massive star's total mass might the inert iron core constitute just before the star undergoes core collapse?

Answer

Between 20 to 30%

The inert, non-radiating iron core in these high-mass stars can accumulate to constitute a significant portion of the star's total bulk, potentially reaching between 20 to 30% of its mass just before the final event.

What percentage of a massive star's total mass might the inert iron core constitute just before the star undergoes core collapse?
Corestarmassive