The binding energy for the following nuclear reactions are expressed in MeV . 2 He 3 + 0 n 1 rightarrow 2 He 4 +20 MeV 2 He 4 + 0 n 1 rightarrow 2 He 5 -0.9 MeV If X 3 , X 4 , X 5 denote the stability of 2 He 3 , 2 He 4 and 2 He 5 , respectively, then the correct order is :

Physics · Nuclear Physics

JEE Main 2026 — 24 January, Evening Shift — Question 36

The binding energy for the following nuclear reactions are expressed in MeV . ${ }_{2} \mathrm{He}^{3}+{ }_{0} \mathrm{n}^{1} \rightarrow{ }_{2} \mathrm{He}^{4}+20 \mathrm{MeV}$ ${ }_{2} \mathrm{He}^{4}+{ }_{0} \mathrm{n}^{1} \rightarrow{ }_{2} \mathrm{He}^{5}-0.9 \mathrm{MeV}$ If $\mathrm{X}_{3}, \mathrm{X}_{4}, \mathrm{X}_{5}$ denote the stability of ${ }_{2} \mathrm{He}^{3},{ }_{2} \mathrm{He}^{4}$ and ${ }_{2} \mathrm{He}^{5}$ , respectively, then the correct order is :

Option A:
$X_{4}>X_{5}>X_{3}$
Correct
Option B:
$X_{4}=X_{5}=X_{3}$
Option C:
$X_{4} > X_{5} < X_{3}$
Option D:
$X_{4} < X_{5} < X_{3}$

Answer: A

Step-by-step solution

$\mathrm{BE}_{\mathrm{He}^{4}}-\mathrm{BE}_{\mathrm{He}^{3}}=20 \mathrm{MeV}$

\mathrm{BE}_{\mathrm{He}^{5}}-\mathrm{BE}_{\mathrm{He}^{4}}=-0.9 \mathrm{MeV} \end{gathered}$$ From eq (1) \& (2) $\mathrm{BE}_{\mathrm{He}^{4}}>\mathrm{BE}_{\mathrm{He}^{5}}>\mathrm{BE}_{\mathrm{He}^{3}}$ $X_{4}>X_{5}>X_{3}$

Answer key and solution verified before publishing.

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Exam: JEE Main 2026
Paper: 24 January, Evening Shift
Subject: Physics
Chapter: Nuclear Physics
Topic: Mass Defect, Binding Energy and Q-Value of Nuclear Reaction