Identify anionic complex from following
Bis (ethylene diamine) dithiocyanatoplatinum (IV)
In Sodiumhexanitrocobaltate (III), the negative charge is carried by the "hexanitrocobaltate (III)" ion. The presence of the sodium cation (Na+) balances the charge of the anionic complex.
Therefore, the correct option is (D) Sodiumhexanitrocobaltate (III).