An atom cannot have two nuclei because the nucleus of an atom is defined as the central, positively charged core of the atom that contains protons and neutrons. The nucleus is held together by strong nuclear forces, which bind the protons and neutrons together.
The stability of an atom is maintained by a delicate balance between the attractive nuclear forces that hold the nucleus together and the repulsive electrostatic forces between positively charged protons. If there were two nuclei within an atom, the positive charges of the protons in each nucleus would repel each other strongly due to the electrostatic forces. This repulsion would overcome the attractive nuclear forces, making the system highly unstable.
Furthermore, the nucleus of an atom contains the majority of its mass. If there were two nuclei, the distribution of mass within the atom would be disrupted, leading to an imbalance and lack of stability.
In nature, the presence of two nuclei within a single atom is not observed. However, under extreme conditions, such as in certain nuclear reactions or during nuclear fission and fusion processes, nuclei can split or combine, resulting in the formation of different elements or isotopes.