C-10-Q115mediumsingle_mcqThe chemical formula of rust is—aFe2O3⋅nH2O\mathrm{Fe_2O_3 \cdot nH_2O}Fe2O3⋅nH2ObFe3O4\mathrm{Fe_3O_4}Fe3O4cFeOdFeCl3\mathrm{FeCl_3}FeCl3