Answer:
FeSO4.
Step-by-step explanation:
We divide the percentages by the relative atomic masses of the elements:
Iron = 36.76 / 55.845= 0.6583
Sulphur = 21.11 / 32.06 = 0.6584
Oxygen = 42.13 / 15.999 = 2.6333
Simplifying the ratios:
Fe : S : O =
0.6583: 0.6584: 2.6333
= 1 : 1 : 4
The empirical formula is FeSO4. (Ferrous Sulphate).