Higher principal energy levels consist of orbitals which are larger in size than the orbitals from lower energy levels. The effect of the greater number of principal energy levels outweighs the increase in nuclear charge and so atomic radius increases down a group.
I think the correct answer from the choices listed above is option C. New nuclei and neutrons result from <span>the splitting of an atom's nucleus. It is called nuclear fission where atoms are being split into smaller parts. Hope this answers the question. Have a nice day.</span>