Why are more neutrons in the nucleus required as the atomic number increases?

• A. To increase binding energy per nucleon
• B. To counteract electrostatic repulsion between protons
• C. To decrease the nucleus mass
• D. To determine the chemical properties

Answer: (B)

The nucleus is held together by the strong nuclear force, which binds nucleons (protons and neutrons), while protons repel each other due to their positive charge. As the atomic number grows, there are more protons and the electrostatic repulsion among them increases. To keep the nucleus stable, you need more neutrons because neutrons don’t add electric charge but do participate in the strong force. They provide additional attractive interactions that help bind protons and other neutrons together, increasing the overall binding energy. Since the strong force is short-range and saturates, adding protons alone would raise repulsion faster than binding unless more neutrons are included. So the neutron-to-proton ratio increases with Z to maintain stability, leading to heavier nuclei having more neutrons than protons.