let me just draw whats happening to the carbon, carbon goes from minus four which means its hogging four electrons to a situtation where its having four electrons being hogged from it, its kind of giving away four electrons, so somewhere in this process, this guy must have given away eight electrons, this is a difference of eight electrons, so plus eight electrons, so what's happened to carbon, carbon has been..., has it been oxidized or has it been reduced, its charge had gone up, so it hasn't been reduced, another way you could say electrons have been taken away from it so it has been oxidized, oxidized, carbon had been oxidized, now lets look at the oxygen, oxygen, over here you have four oxygen molecules, i'll just write four oxygen molecules, and they all have an oxidation state of zero, because from an oxidation number point of view they are neutral, and on this side we have two, no we have four oxygen molecules, and what's there oxidation state?