In the following compound why is Fe written as iron and not ferrate? Also what does the (II) in the middle of Hexamamminenickel(II)chloride represent?

Dear student

If the coordination sphere of the complex compound has negative charge, the name of the central metal atom ends in ate and the oxidation number of the central metal atom is written in Roman numerals in brackets. In case of Fe, the latin name , Ferrate is used.
The  bracket contains the oxidation number of the metal

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