Answer: Transmutation
Explanation: Combustion, polymerization and neutralization are reactions that depends on electron exchange and molecular bonds rearrange. However, change the nucleus implies change the number of protons which requieres a lot of energy and also change the identity of the element.
Elements are defined by the number of protons in the nucleus, because this is a heavy particle compare to electron and the interaction between them gives special properties.
Breaking nucleus of an atom to transform into other is the principle of nuclear reactions, and the process that take place is transmutation.