Final answer:
An unstable Fe-53 nucleus is likely to undergo beta decay, emitting a high-speed electron (beta particle) and becoming a cobalt nucleus.
Step-by-step explanation:
The unstable Fe-53 nucleus will most likely undergo beta decay, which is a type of radioactive decay that unstable nuclei experience when their neutron to proton ratio is too high. During beta decay, a neutron in the nucleus is transformed into a proton and an electron. The electron, also known as a beta particle, is then emitted from the nucleus at high speed.
This mechanism serves to decrease the neutron to proton ratio of the nucleus, thereby moving it toward a more stable situation. After the beta decay, the resulting nucleus will thus have one more proton than before, changing the element from iron (Fe) to cobalt (Co), while the mass number remains unchanged.