What is the O.N. of Fe and S in FeS2 (iron pyrite)?

You are correct in that the Fe is oxidized from +2 to +3 as in (i).

Sulfur is tricky because it can assume so many oxidation states, plus and minus. In the iron disulfide, it has a -1 and is oxidized to +4 as you have in (ii). So both of the species are oxidized as you have stated. I have seen redox reactions where one sulfur was oxidized from one compound and one was reduced from another, so this is OK!

IIRC, iron pyrite is FeS, no longer FeS2 (i do no longer think of that Fe(IV) is a valid oxidation state of iron, the two). we could understand the place you ar having subject with this subject. Please attempt to artwork on it your self and let us know the place you're turning out to be caught (if that's on the beginning up, no subject, we will coach you ways to thru it). right this is a sprint to get you all started: initiate with the help of writing the unbalanced equation for the reaction of iron pyrite and oxygen to form SO2 and Fe2O3.