If 100 g of iron reacts with excess oxygen,how much rust should be produced

Answer 1

Rust is a complex hydrated iron oxide. For purposes of this problem we'll call it Fe2O3.
..................4Fe + 3O2 ==> 2Fe2O3
mols Fe = grams/atomic mass = 100/55.85 = 1.8
Convert mols Fe to mols Fe2O3 this way.
1.8 mols Fe x (2 mols Fe2O3/4 mols Fe) = 0.9 mols Fe2O3
grams Fe2O3 = mols Fe2O3 x molar mass Fe2O3 = ?