From the binding energy per nucleon versus mass number curve:
(A) B.E/nucleon is small for light nuclei like \( {}^{1}_{1}\mathrm{H},\ {}^{2}_{1}\mathrm{H},\ {}^{3}_{1}\mathrm{H} \)
(B) B.E/nucleon decreases in heavy nuclei making them less stable.
(C) When two light nuclei combine to form heavy nucleus, energy is absorbed.
(D) Heavy nucleus splits into lighter nuclei which results in liberation of energy.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (B), (D) only
The binding energy per nucleon curve rises steeply for the lightest nuclei, is nearly flat around 8 MeV in the middle, and then falls slowly for heavy nuclei. Energy is released whenever nuclei move to a higher binding energy per nucleon.
(A) B.E/nucleon is small for light nuclei like \( {}^{1}_{1}\mathrm{H},\ {}^{2}_{1}\mathrm{H},\ {}^{3}_{1}\mathrm{H} \) — Correct. For nuclei with \( A\lt30 \) the value is below 8 MeV, and for the hydrogen isotopes it is only about 1 to 3 MeV.
(B) B.E/nucleon decreases in heavy nuclei making them less stable — Correct. Beyond the peak near iron the value falls (to about 7.6 MeV for A = 238), so heavy nuclei are less tightly bound.
(C) When two light nuclei combine to form heavy nucleus, energy is absorbed — Incorrect. The fused nucleus has a higher binding energy per nucleon, so the system becomes more tightly bound and energy is released (fusion).
(D) Heavy nucleus splits into lighter nuclei which results in liberation of energy — Correct. The fragments have a higher binding energy per nucleon than the heavy nucleus, so the difference is released (fission).
NCERT (2026-27):
Nuclear Binding Energy – “… (ii) Ebn is lower for both light nuclei (A<30) and heavy nuclei (A>170).”
Nuclear Energy – “… 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.)”