The correct statement about the balanced equations for nuclear and chemical changes is:
A nuclear equation is balanced according to mass number. A chemical equation is balanced according to the number of atoms before and after the change.
In nuclear reactions, both atomic numbers and mass numbers must be balanced, but the mass number is often the primary focus since it accounts for the nucleons involved (protons and neutrons). In contrast, chemical equations balance the number of atoms of each element before and after the reaction, as the mass is conserved.