4 Fe + 6 H₂O + 3 O₂ → 4 Fe(OH)₃


Police found 10 grams of Fe(OH)₃ on the knife. Convert grams of rust (Fe(OH)₃) into grams of iron (Fe) to see if the knife contained enough to murder the butler.



345 g Fe



5.22 g Fe



7.34 g Fe



2.95 g Fe