Answer
$$2.23 \mathrm{\ MeV}
$$
Work Step by Step
Now third step: $^{2} \mathrm{H} \rightarrow p+n,$ which rewritten as $^{2} \mathrm{H} \rightarrow^{1} \mathrm{H}+n .$ The work required is
$$
\begin{aligned} \Delta E_{3} &=\left(m_{\mathrm{tH}}+m_{n}-m_{2 \mathrm{H}}\right) c^{2}=(1.00783 \mathrm{u}+1.00867 \mathrm{u}-2.01410 \mathrm{u})(931.5 \mathrm{MeV} / \mathrm{u}) \\ &=2.23 \mathrm{MeV} \end{aligned}
$$
