(i) Complex [Co(NH3)6]‌‌[Cr(CN)6] shows coordination isomerism. This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in the complex.
(ii) In [Ni(H2O)6]2+,H2O is a weak field ligand. So there are unpaired electrons in Ni2+. In this complex, the d electrons from the lower energy level can be excited to the higher energy level. The possibility of d - d electrons is present. Therefore, Ni(H2O6)]2+ is coloured. In [Ni(CN)4]2−, the electrons are all paired as CN−is a strong ligand. So, d−d transition is not possible in [Ni(CN)4]2−. Hence, it is colourless.
(iii) The IUPAC name of [Co(NH3)5(CO3)]‌Cl is Pentaamminecarbonatocobalt (III) chloride.