Which of the following isotopes would you expect to be stable?

• A. Ra-226
• B. C-12
• C. H-3
• D. U-238

Answer: (B)

Verified step by step guidance

1. Understand that isotope stability depends on the ratio of neutrons to protons in the nucleus and the overall nuclear binding energy.
2. Recall that light elements tend to be stable when the neutron-to-proton ratio is close to 1, while heavier elements require a higher neutron-to-proton ratio for stability.
3. Analyze each isotope: C-12 has 6 protons and 6 neutrons (ratio 1:1), which is known to be very stable; H-3 (tritium) has 1 proton and 2 neutrons, which is radioactive; Ra-226 and U-238 are heavy isotopes that are radioactive despite their neutron-rich composition.
4. Use the concept that stable isotopes generally do not undergo radioactive decay, so isotopes like C-12 are stable, while H-3, Ra-226, and U-238 are radioactive and thus unstable.
5. Conclude that among the given options, C-12 is the stable isotope based on its balanced neutron-to-proton ratio and known nuclear stability.