Answer
$Na(s) + \frac{1}{2}Br_2(l) --> NaBr(s)$
$\Delta H ^o _f (NaBr(s)) : -361.4 kJ/mol$
Work Step by Step
1. Write the unbalanced equation:
$Na(s) + Br_2(l) --> NaBr(s)$
2. Balance it:
$Na(s) + \frac{1}{2}Br_2(l) --> NaBr(s)$
3. The $\Delta H ^o _ f $ value is found in the book's final pages.