The correct option is
D A -> d, B -> c, C -> b, D -> a
PolymerizationIsomerism : This is not true isomerism because it occurs between compounds having the same empirical formula, but different molecular weights.
For example, [Pt(NH3)2CI2],[Pt(NH3)4][PtCI4],[Pt(NH3)4][Pt(NH3)CI3]2.
InonizationIsomerism : This type of isomerism is due to the exchange of groups between the complex ion and the ions outside it. [Co(NH3)5Br]SO4 is red-violet. An aqueous solution gives a white precipitate of BaSO4 with BaCI2 solution, thus confirming the presence of free SO2−4 ions. In contrast [Co(NH3)5SO4]Br is red. A solution of this complex does not give a positive sulphate test with BaCI2.It does give a cream-coloured precipitate of AgBr with AgNO3, thus confirming the presence of free Br− ions.
LinkageIsomerism : Certain ligands contain more than one atom which could donate an electron pair. In the NO−2 group in the complex ion. In the NO−2 ion, either N or O atoms could act as the electrons pair donor. Thus there is the possibility of isomerism. Two different complexes [Co(NH3)5NO)2]Cl2 and [Co(NH3)5(ONO)]Cl2 have been prepared, each containing the NO−2 group in the complex ion.
CoordinationIsomerism : If the complex is a salt having both cation and anion as complex ions then the ligands can exchange position between the cation and the anion. This will result in the formation of coordinates isomers. For example
[Co(en)3][Cr(C2O4)3] and [Co(en)2(C2O4)][Cr(en)(C2O4)2]
[Cr(en)2(C2O4)][Co(en)(C2O4)2] and [Cr(en)3][Co(C2O4)3]