a change in the number of protons or neutrons occurs in which type of reaction

a change in the number of protons or neutrons occur in a nuclear reaction, ; fusion or fission . Protons and neutron are subatomic particles found in the nucleus of an atom, any reaction that can alter the number of protons or neutrons are therefore called nuclear reactions.

Change in number of proton change the atomic number ( nuclear charge) while change in neutron number change the atomic mass( mass number).

 Fission is when a large atom split into two lighter atoms (nuclei)  while fusion is when  two smaller nuclei come together to form a single atom, both the process result in change in both the number of protons ( atomic number or nuclear charge ) and number of neutrons (atomic mass). Likewise process like radioactive decay can result to change in both number of protons and neutrons, alpha decay can will result to loss of two protons and two neutrons while beta minus decay will can change neutron into a proton while a beta plus decay  will change a proton into neuron.