What is the oxidation numbers of each element in the #[Fe(C-=N)_6]^(2+)# complex?
The Cyanide part must be
The ion is called 'hexacyano-ferrate(II)' There also exists an ion called 'hexacyano-ferrate(III)', with an overall charge of
Remove the cyanide ligands sequentially, and you get to
You have the coordination complex
As regards the oxidation numbers of
Around nitrogen, there are 5 valence electrons (2 from its lone pair, and 3 electrons from its contribution to the triple bond); that, with 2 inner core electrons, and 7 nuclear protons, means its charge is neutral. Thus nitrogen has a FORMAL oxidation number of 0 in the cyanide anion. Now of course, the sum of the oxidation numbers must equal the charge on the ion; so the oxidation number of
To do it the long way, there are 3 electrons around
Note (i) that
Note (ii) that some common laboratory solvents can pass thru skin, along with whatever salts are dissolved in the solvent.