What kind of isomerism exists between [Cr(H2O)6]Cl3 (violet) and [Cr(H2O)5Cl]Cl2.H2O (greyish−green)?
(a) Linkage isomerism
(b) Solvate isomerism
(c) Ionisation isomerism
(d) Coordination isomerism
Answer: (b). Solvate isomerism
Solute isomerism to shown when two compounds having the same molecular formula differ by whether it has solvent molecule is directly bonded to a metal ion or is present as free solvent molecules in the crystal lattice.
When water is present as a solvent and shows this type of isomerism then it is known as hydrate isomerism or Solvate isomerism.
Coordination compound [Cr(H2O)6]Cl3 and [Cr(H2O)5Cl]H2O.Cl2 are solvate isomers, because water is exchanged by chloride ion. This is why both of them show different colour on exposure to sunlight.