Solution:
Mass defect \(\Delta m = (2 m_p + 2 m_n) - m_{\text{He}} = [2(1.0073) + 2(1.0087)] - 4.0015 = 0.0305\text{ u}\). Binding energy is \(E_b = \Delta m \times 931.5\text{ MeV} \approx 0.0305 \times 931.5 \approx 28.4\text{ MeV}\).
The mass of a proton is \(1.0073\text{ u}\) and that of neutron is \(1.0087\text{ u}\) (\(u = \text{atomic mass unit}\)). The binding energy of \({}_2\text{He}^4\) is (mass of helium nucleus = \(4.0015\text{ u}\))
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