What is the oxidation state of Au & C in AuC?

Well for Carbon there is like a golden rule: you don't know the oxidation state of carbon by itself because it can vary so much from like +2 in CO to CH4: +4. So we have to go by what the oxidation state of gold is usually which is +1 because only needs one to fulfill its completeness of its d orbitals. So go off how many electrons Gold has to lose and I think you should be set.

And even if you have -4 for carbon and +4 for gold, metals always lose I don't think I have ever seen a metal gain electrons so forget about a negative oxidation state on a metal anywhere because metals are a sea of electrons remember so they want to lose electrons. And +4 doesn't work for gold because if you lose 4 electrons you are actually causing more of an entropy change than if you were to just lose one electron as in the +! oxidation state.