The HEXACYANIDOFERRATE(II) ion $[\mathrm{Fe(CN)_6}]^{4-}$ contains iron in oxidation state

1. The hexacyanidoferrate(II) IUPAC suffix '-(II)' explicitly tells us the iron oxidation state — but let's compute it as a check. 2. Total charge on the complex ion: $-4$. 3. Six $\mathrm{CN^-}$ ligands contribute $-6$ total charge. 4. Let Fe oxidation state be $x$: $x + 6(-1) = -4 \Rightarrow x = +2$. 5. So iron is in the $+2$ state, consistent with the (II) in the name. 6. This ion forms the famous ferrocyanide salts — yellow prussiate of potash, $K_4[\mathrm{Fe(CN)_6}]$. 7. Options A, C, D would all require a different complex charge. _Source: syllabus Chemistry Part 1, Ch 5, §5.3 (Oxidation state calculation + nomenclature consistency), p. 4–5._