Question

Iron pyrite (fool's gold) is iron (lI) sulfide. What is its formula?

Answer 1

Iron pyrites is `"iron persulfide"`, `FeS_2`, with a formal `Fe(II+)` oxidation state.

Explanation:

The sulfur binds as a `"persulfide"`, i.e. `""^(-)S-S^-`; think `"peroxide"`, `O_2^(2-)`. The formal oxidation state of `S` here is `-I`.