Which process produces the largest amount of energy given off by stars?

The answer is nuclear fusion.

Nuclear fusion is the process that produces the energy in the stars. The simplest example of this process is the hydrogen-to-helium fusion, where two nuclei of hydrogen combine together into a nucleum of helium. In the process, a huge amount of energy is released, according to Einstein's famous equivalence:

where m is the mass difference between the total mass of the initial nuclei and the mass of the final products, and c is the speed of light.

B) raising the temperature and reducing the volume of the gas.|-/ 

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