Al2O3

Mr (Al2O3) = 2 Ar (Al) + 3 Ar (O) = 2 * 27 + 3 * 16 = 102

W (Al) = nAr (Al) / Mr (Al2O3) * 100% = (2 * 27) / 102 * 100% = 52,94%

Fe2O3

Mr (Fe2O3) = 2 Ar (Fe) + 3 Ar (O) = 2 * 56 + 3 * 16 = 112 + 48 = 160

W (Fe) = nAr (Fe) / Mr (Fe2O3) * 100% = (2 * 56) / 160 * 100% = 70%

Cr2O3

Mr (Cr2O3) = 2 Ar (Cr) + 3 Ar (O) = 2 * 52 + 3 * 16 = 152

W (Cr) = nAr (Cr) / Mr (Cr2O3) * 100% = (2 * 52) / 152 * 100% = 68,42%

Отже:

W (Fe) > W (Cr) > W (Al), бо

70% > 68,42% > 52,94%