As gravity continues to crush the inner core, the fusion of carbon and oxygen begins. what temperature is needed for the fusion of carbon and oxygen into heavier elements?

600,000,000 degree C

Explanation:

This stage is the last stage and is refereed to as supernova. In the beginning of this stage, gravity pulls the inner core and crush it, due to which fusion of atoms starts. Carbon and Oxygen fuse together and the temperature is about of 600,000,000 degree C.

The most heavier atom that can be formed out of this fusion is the iron. The moment all the atoms becomes of iron, no further fusion is possible hence that body emits radiation of high intensity and collapse causing a big supernova.

a lot of it means it can be "burned" for energy and sold at one price. if it is scarce, the price will go up