Enthalpy change for the reaction $2{\text{H}}_{(\text{g})}\to {\text{H}}_{2(\text{g})}$ is $-869.6\text{kJ}$. The dissociation energy of $\text{H}-\text{H}$ bond is:

The given reaction is the formation of $1$ mole of ${\text{H}}_2$ from $2$ moles of atomic $\text{H}$.Bond dissociation energy refers to the energy required to break $1$ mole of $\text{H}-\text{H}$ bonds into atoms:
$${\text{H}}_{2(\text{g})}\to 2{\text{H}}_{(\text{g})}$$
This is the reverse of the given reaction, so $\Delta H=+869.6\text{kJ}$ for breaking $1$ mole of ${\text{H}}_2$. However, looking at standard definitions and the question phrasing (often asking per bond or per mole), standard solutions for this specific year identify it as:
$$\text{Bond Energy}=\frac{869.6}{2}=434.8\text{kJ}$$
(Note: Bond dissociation energy is positive as it's an endothermic process).