Carbon oxidation number

To find the oxidation number of an atom in a compound you have to look at the other atoms in the compound and follow some general rules. Let's start with CN, This compound actually has a charge of -1 because the carbon and nitrogen share a triple bond leaving carbon one bond short. Carbon has 3 common oxidation states of -4, +2 and +4... if carbon was in the -4 state nitrogen would have to be in the +3 state to leave a total charge of -1. +3 is one of the common oxidation state for nitrogen so this might well be your answer. As for CNO, Oxygen always has an oxidation state of -2 (unless bonded to F or another O) so we know that oxygen is in the -2 state and the carbon is now has it's beloved 4 bonds so the molecule has no charge. This means the combined oxidation states of C and N must be +2. As we know from before carbon is happy in the +2 state but not the +1 state and neither is nitrogen... but this is ok as Nitrogen is happy in the +0 state (Common oxidation states for nitrogen are -3, -2, -1, 0, +2, +3, +4 and +5). So for CNO the oxidation number for C is +2