According to the binding energy per nucleon vs mass number curve, B.E./A of different nuclei are different. Arrange the following nuclides in decreasing order of B.E. per nucleon.
(A) 238U
(B) 7Li
(C) 56Fe
(D) 4He
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (C), (A), (D), (B)
The binding energy per nucleon curve rises steeply for light nuclei, peaks at about 8.8 MeV near A = 56 (iron), and then falls slowly for heavy nuclei as the Coulomb repulsion between protons grows. 4He is unusually high for so light a nucleus, because it is especially tightly bound.
\( \text{(C) } {}^{56}\mathrm{Fe}: \approx 8.8\,\mathrm{MeV} \)
\( \text{(A) } {}^{238}\mathrm{U}: \approx 7.6\,\mathrm{MeV} \)
\( \text{(D) } {}^{4}\mathrm{He}: \approx 7.1\,\mathrm{MeV} \)
\( \text{(B) } {}^{7}\mathrm{Li}: \approx 5.6\,\mathrm{MeV} \)
So the decreasing order is (C), (A), (D), (B).
NCERT (2026-27):
Nuclear Binding Energy – “… Figure 13.1 is a plot of the binding energy per nucleon \( E_{bn} \) versus the mass number \( A \) for a large number of nuclei. … The curve has a maximum of about 8.75 MeV for \( A = 56 \) and has a value of 7.6 MeV for \( A = 238 \). (ii) \( E_{bn} \) is lower for both light nuclei \( (A \lt 30) \) and heavy nuclei \( (A \gt 170) \).”
