Which of the following isomeric pairs shows ionization isomerism?

Options

A. `[Co(NH_(3))_(6)][Cr(CN)_(6)]` and `[Cr(NH_(3))_(6)][Co(CN)_(6)]`
B. `[Cr(H_(2)O)_(6)Cl_(3)` and `[Cr(H_(2)O)_(5)Cl]Cl_(2).H_(2)O`
C. `[Pt(NH_(3))_(2)Cl_(2)]` and `[Pt(NH_(3))_(4)][PtCl_(4)]`
D. `[Co(NH_(3))_(5)Br]SO_(4)` and `[Co(NH_(3))_(5) SO_(4)]Br`

Answer

4

Explanation

In (4) primary valency groups are different.