Ionisation isomerism is possible with

Explanation

Ionisation isomerism occurs when the same compound can form different ions in solution. This happens when there is a coordination compound where the counter ions (like chloride, bromide, etc.) can exchange positions with ligands in the coordination sphere.

[Co(NH₃)5Cl]Br can exhibit ionisation isomerism because it can dissociate in different ways in solution:

• One form could dissociate into [Co(NH₃)5Cl]²⁺ and Br⁻.
• Another form could dissociate into [Co(NH₃)5Br]²⁺ and Cl⁻.

This results in two isomers with different ionic compositions, exhibiting ionisation isomerism.

The other options:

• [Co(NH₃)6]Cl3 and [Co(NH₃)3Cl₃] do not exhibit ionisation isomerism because the counter ions (Cl⁻) are already fixed and cannot exchange with ligands.
• [Co(H₂O)6]Cl3 also does not show ionisation isomerism since the chloride ions are not part of the coordination sphere but are merely counterions.

Final Answer

Thus, ionisation isomerism is most likely in [Co(NH3)5Cl]Br.