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.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.