Final answer:
Fusion requires a temperature of 15 million degrees Celsius to occur.
Step-by-step explanation:
The process that requires a temperature of 15 million degrees Celsius to occur is Fusion.
Fusion is the process of combining lighter nuclei to make heavier nuclei. It occurs at extremely high temperatures where all molecules dissociate into atoms, forming plasma. These conditions are found in stars, which are powered by fusion reactions.
Humans have achieved temperatures high enough for fusion to occur on a large scale in thermonuclear weapons, such as hydrogen bombs. These weapons contain a nuclear fission bomb that, when exploded, releases enough energy to produce the extremely high temperatures necessary for fusion to occur.