What is the limiting reactant for each amount of reactants in the following reaction: 2Na (s) + Br2 (g) -> 2 NaBr (s)

a) 2 mol Na, 2 mol Br2
b) 2.5 mol Na, 1 mol Br2
c) 1.8 mol Na, 1.4 mol Br2
d) 12.6 mol Na, 6.9 mol Br2