What is the heaviest element that can be fused in the core of a star?

The heaviest element which can be fused in the 'core of a star is iron'.

Explanation:

Throughout a stars lifetime, there is a 'continuous fusion reaction' going on in its core. This reaction is fed by various elements present near the core of the star.These elements can most probably be hydrogen, helium, carbon, oxygen, nickel, and iron. When the star runs out of one elements, it uses the other to continue the fusion reaction going on in its core.

Probably north korea if your family has decided to use only nuclear power.

This country likely has a high total fertility rate (tfr).