Seth learned in school that iron reacts with oxygen in the air to form iron oxide. The chemical equation is: Fe + O2 à FeO2
Seth wanted to see if this would really happen, so he put 13 grams of tiny iron (Fe) pieces on the window sill outside his house. After two weeks, he saw that the iron no longer looked shiny. He checked the mass of the pieces and saw that it went from 13 to 21 grams. Seth’s friend said this shows that matter is not conserved.

Do you agree or disagree with Seth’s friend? Write a scientific explanation to support your position.