Select ALL cases in which the AVERAGE oxidation number of the element named is a non-integer. Use O = $-2$, H = +1, and count all atoms of that element in the formula.

1. AFe in $\mathrm{Fe}{}_3\mathrm{O}{}_4$
2. BC in $\mathrm{C}{}_3\mathrm{O}{}_2$
3. CN in $\mathrm{NH}{}_4\mathrm{NO}{}_3$ (average over both N atoms)
4. DS in $\mathrm{S}{}_4\mathrm{O}{}_6{}^{2-}$