What happens when nuclei with less total binding energy transform to nuclei with greater binding energy?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Energy is released.
Every nucleus has a mass defect, and its binding energy is the energy equivalent of this defect. So the greater the binding energy, the less is the total mass of the bound system.
Option (1) Energy is consumed. — Incorrect. Energy has to be supplied only for the reverse change, from nuclei of greater binding energy to nuclei of less binding energy.
Option (2) Energy remains the same. — Incorrect. The products have less total mass than the original nuclei, and this mass difference must appear as energy.
Option (3) Energy is released. — Correct. The number of protons and neutrons stays the same. But the final nuclei are more tightly bound and lighter. So the gain in binding energy is given out as a net energy release.
Option (4) It depends upon the nuclei. — Incorrect. Any change to greater total binding energy releases energy. This holds when a heavy nucleus splits into intermediate mass fragments (fission). It also holds when light nuclei join into a heavier one (fusion).
NCERT (2026-27):
Nuclear Energy – “… Now, the greater the binding energy, the less is the total mass of a bound system, such as a nucleus. Consequently, if nuclei with less total binding energy transform to nuclei with greater binding energy, there will be a net energy release. This is what happens when a heavy nucleus decays into two or more intermediate mass fragments (fission) or when light nuclei fuse into a havier nucleus (fusion.)”