6.52 g of oxygen gas reacts with some amount of iron, and 11.50 g of Fe2O3 are formed. What was the amount of iron that reacted with the oxygen?

Answer 1

4Fe + 3O2 ==> 2Fe2O3

mols Fe2O3 = grams/molar mass
Using the coefficients in the balanced equation, convert mols Fe2O3 to mols
Fe in the equation.
You want grams Fe? Convert mols Fe to g. g = mols Fe x atomic mass Fe.

Note that the grams 6.52 O2 is not relevant.