Arrange the following nuclei in the increasing order of their binding energy per nucleon.
\( {}^{4}_{2}\mathrm{He},\ {}^{6}_{3}\mathrm{Li},\ {}^{56}_{26}\mathrm{Fe},\ {}^{238}_{92}\mathrm{U} \)
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Li, He, U, Fe
The binding energy per nucleon rises steeply for the lightest nuclei, reaches a maximum of about 8.8 MeV near iron (\( A\approx56 \)), and then falls slowly for heavy nuclei. Use the standard values.
\( {}^{6}_{3}\mathrm{Li} \): about 5.3 MeV per nucleon
\( {}^{4}_{2}\mathrm{He} \): about 7.1 MeV per nucleon
\( {}^{238}_{92}\mathrm{U} \): about 7.6 MeV per nucleon
\( {}^{56}_{26}\mathrm{Fe} \): about 8.8 MeV per nucleon
So the increasing order is Li (5.3) < He (7.1) < U (7.6) < Fe (8.8).
NCERT (2026-27):
Nuclear Binding Energy – “… Figure 13.1 is a plot of the binding energy per nucleon Ebn 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) Ebn is lower for both light nuclei (A<30) and heavy nuclei (A>170).”
