The mass defect of the nuclear reaction: <br> is — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

In positron decay, using nuclear masses: $\Delta m_{nucl} = m_{nucl}(\text{Be}) + m_e - m_{nucl}(\text{B})$. Substituting atomic masses ($M$): $\Delta m = (M_{Be} - 4m_e) + m_e - (M_B - 5m_e) = M_{Be} - M_B + 2m_e$. Therefore, correct answer is D.