Write for empiricalformula
Fe2+, cr4+, cl-, O2-

{eq}Fe^{2+} {/eq} and {eq}I^- {/eq} forms {eq}FeI_2 {/eq}

{eq}Fe^{2+} {/eq} and {eq}S^{2-} {/eq} forms {eq}FeS {/eq}

{eq}Cr^{4+} {/eq} and...

Explanation:

Empirical formula:

The empirical formula gives the simple ratio of the different types of atoms in a compound. It is different from the molecular formula, which gives the exact number of each type of atom in a compound.