Question

Which would result in radioactive decay? Check all that apply.

a neutron-to-proton ratio of 1:1 in a small nucleus

a neutron-to-proton ratio of 1:2 in a large nucleus

a nucleus that contains 90 protons and 100 neutrons

a nucleus that contains 8 protons and 8 neutrons

any isotope of the element uranium, which has atomic number 92

any isotope of the element potassium, which has atomic number 19

Answer 1

Answers: 2, 3, and 5.

Brief reasons:
- a neutron:proton ratio of 1:1 in a small nucleus — usually stable (light nuclei favor N/Z ≈ 1), so no decay.
- a neutron:proton ratio of 1:2 in a large nucleus — proton-rich and strongly unstable; will undergo radioactive decay (β+ / electron capture or other proton-decay modes).
- 90 protons and 100 neutrons (Z=90, N/Z ≈ 1.11) — far neutron-poor for such a heavy element, so unstable and radioactive.
- 8 protons and 8 neutrons (O-16) — stable, not radioactive.
- any isotope of uranium (Z=92) — true: all uranium isotopes are radioactive.
- any isotope of potassium (Z=19) — false: potassium has stable isotopes (e.g., K-39, K-41), so not every isotope is radioactive.