Answer
Na is the limiting reactant.
Work Step by Step
Determine the limiting reactant. Choose one of the reactants and determine how much we need compared to how much is available. We choose to compare Na.
$12.6$ $mol$ $Na (avaliable)$
$6.9 mol$ $Br_{2}$$\times\frac{2 mol Na}{1 mol Br_{2}}$ $=13.8$ $mol$ $Na (needed)$
