The heaviest element to be created by exothermic nuclear fusion is: oxygen
carbon
iron
helium

The heaviest element to be created by exothermic nuclear fusion is Iron

Explanation:

Because it is the heaviest element produced during fusion without having to add energy, and it is the lightest element produced during fission without having to add energy. Energy-wise, everything in the universe wants to be iron! Iron is the most abundant element on Earth, making up 34.5 percent of Earth's mass.

space exploration has led to the development and technological improvement of many everyday items. (if this answer is wrong i will find the right answer) : )