The correct option is C Potassium ferrocyanide
Only 'Potassium ferrocyanide' (K4[Fe(CN)6]) show properties of coordination compound.
When it gets dissolve they do not form simple ion like Fe+2 or CN−, but instead their complex ions remain intact.
whereas carnallite (KMgC13), Gypsum (CaSO4) and Ferrous ammonium sulphate ((NH4)2Fe(SO4)2) they dissovle and give simple ions.
Option (c) is correct.