b
\(\frac{1}{0} \mathrm{n} \longrightarrow \frac{1}{1} \mathrm{H}+_{-1} \mathrm{e}^{0}+\overline{\mathrm{v}}+Q\)

The mass defect during the process

\(\Delta m=m_{n}-m_{H}-m_{e}\)

\(=1.6725 \times 10^{-27}-\left(1.6725 \times 10^{-27}+9 \times 10^{-31} \mathrm{kg}\right)\)

\(=-9 \times 10^{-31} \mathrm{kg}\)

The energy released during the process

\(E=\Delta \mathrm{mc}^{2}\)

\(E=9 \times 10^{-31} \times 9 \times 10^{16}=81 \times 10^{-15}\,Joules\)

\(E=\frac{81 \times 10^{-15}}{1.6 \times 10^{-19}}=0.511 \mathrm{\,MeV}\)