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Which of the following statements about nuclear physics are correct? (One or more may be correct.)

1. The rest mass of a stable nucleus is less than the sum of the rest masses of its separated nucleons.
2. The rest mass of a stable nucleus is greater than the sum of the rest masses of its separated nucleons.
3. In nuclear fusion, energy is released when two nuclei of medium mass (approximately 100 amu each) combine.
4. In nuclear fission, energy is released when a very heavy nucleus breaks apart into smaller fragments.

Correct answer: The rest mass of a stable nucleus is less than the sum of the rest masses of its separated nucleons.

Solution

A stable nucleus has a mass defect — its rest mass is less than the sum of individual nucleon masses, with the difference appearing as binding energy. Fusion releases energy for light nuclei (like H isotopes), not medium-mass nuclei. Fission releases energy for very heavy nuclei (like U-235). So options A and D are correct.

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