How many moles of oxygen gas react with 2.4 moles of iron in the rusting reaction?
Assuming the formula for rust is Fe2O3 (and that's a simplified formula--it is more complicated than that), then 4Fe + 3O2 --> 2Fe2O3.
moles O2 = 2.4 mols Fe x (3 moles O2/4 mols Fe) = 2.4 x 3/4 = ?