For atoms beyond the first 20, their neutron number can exceed their proton number up to a certain point.

For atoms beyond the first 20, their neutron number can exceed their proton number up to a certain point.

• A. True
• B. False
• C. Not sure
• D. Always

Answer: (A)

The key idea is how the neutron-to-proton ratio affects nuclear stability. Protons repel each other due to Coulomb repulsion, so adding neutrons—boson-like participants that don’t add charge—helps bind the nucleus via the strong force without increasing repulsion. As elements get heavier (beyond about Z = 20), the stable nuclei require more neutrons than protons to stay bound. That means the neutron number often exceeds the proton number for these atoms, so the statement is true. There is a limit set by nuclear stability (the valley of stability): if there are too many neutrons, beta decay can convert neutrons into protons to move toward that balance. Examples of heavier stable nuclei have N > Z, such as iron-56 (Z = 26, N = 30) and nickel-62 (Z = 28, N = 34).

The key idea is how the neutron-to-proton ratio affects nuclear stability. Protons repel each other due to Coulomb repulsion, so adding neutrons—boson-like participants that don’t add charge—helps bind the nucleus via the strong force without increasing repulsion. As elements get heavier (beyond about Z = 20), the stable nuclei require more neutrons than protons to stay bound. That means the neutron number often exceeds the proton number for these atoms, so the statement is true. There is a limit set by nuclear stability (the valley of stability): if there are too many neutrons, beta decay can convert neutrons into protons to move toward that balance. Examples of heavier stable nuclei have N > Z, such as iron-56 (Z = 26, N = 30) and nickel-62 (Z = 28, N = 34).