C-10-Q034mediumsingle_mcqChromite ore has the formula—aFeO⋅Cr2O3\mathrm{FeO \cdot Cr_2O_3}FeO⋅Cr2O3bCr2O3\mathrm{Cr_2O_3}Cr2O3cFeCr2\mathrm{FeCr_2}FeCr2dCr2(SO4)3\mathrm{Cr_2(SO_4)_3}Cr2(SO4)3