What is the heaviest element that can be formed by stellar fusion

iron

Explanation:

Since the heaviest element created in a star by nuclear fusion reactions is iron, a large iron core eventually forms at the center of everything. At this point, gravity becomes overwhelming, the core collapses, and an explosion occurs, during which outer layers of gas and heavy elements are ejected to space.

in most common fires, oxygen is needed for an oxidation reaction to takes place. the combination of oxygen with any element as fuel can create fire and combustion will occur especially if wood, light materials and other combustible things are combine with oxygen.