The pair not correctly matched is:

• A
  $[CoBr(NH_3)_5]SO_4$ and $[CoSO_4(NH_3)_5]Br$ $\Rightarrow$ Ionisation isomerism
• B
  $[Cr(H_2O)_6]Cl_3$ and $[Cr(H_2O)_5Cl]Cl_2 \cdot H_2O$ $\Rightarrow$ Linkage isomerism
• C
  $[Cr(H_2O)_4(NO_2)_2]Cl$ and $[Cr(H_2O)_4(ONO)_2]Cl$ $\Rightarrow$ Linkage isomerism
• D
  $[Cr(H_2O)_5Cl]Cl_2$ and $[Cr(H_2O)_4Cl_2] \cdot Cl \cdot H_2O$ $\Rightarrow$ Hydrate isomerism