The nuclear reaction that occurs by combining two or more lighter atoms into a larger one is called what?
a. nuclear fusion
b. nuclear fission
c. beta emission
d. alpha emission

The nuclear reaction that occurs by combining two or more lighter atoms into a larger one is called nuclear fusion. As a result of this reaction a huge amount of energy is released.  
Nuclear fission is the opposite process of nuclear fusion when the atom splits into several smaller atoms.

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