Which statement about the strong nuclear force is true?

• A. It binds electrons to the nucleus.
• B. It binds quarks together only in protons and neutrons.
• C. It governs gravitational attraction between planets.
• D. It binds protons and neutrons together in the nucleus.

Answer: (D)

The strong nuclear force is the interaction that holds the nucleus together by binding protons and neutrons. It operates at very short distances (around a femtometer) and is strong enough to overcome the electrostatic repulsion between positively charged protons, keeping the nucleus intact. It is not responsible for binding electrons to the nucleus—electrons are held by electromagnetic attraction. It’s also not about gravity, which governs large-scale motions like planets. While the strong force does bind quarks inside protons and neutrons (via gluons), saying it binds quarks only in protons and neutrons isn’t accurate, since quarks are bound inside all hadrons and the relevant nuclear binding involves a residual effect of the strong interaction that acts between nucleons. The statement that protons and neutrons are bound together in the nucleus by this force is the correct emphasis.