What kind of isomerism exists between [Cr(H2O)6]Cl3(violet) and [Cr(H2O)5Cl]Cl2⋅H2O (greyish-green)?

2. Solvate isomerism

3. lonisation isomerism

4. Coordination isomerism

Hint: H2O is replaced by halide ion which is present as counter ion

Solvate isomerism to shown when two compounds having the same molecular formula differ by whether or 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 the solvent and shows this type of isomerism then it is known as hydrate isomerism.

Coordination compound $\left[Cr{\left({H}_{2}O\right)}_{6}\right]C{l}_{3}$ and $\left[Cr{\left({H}_{2}O\right)}_{5}\right]C{l}_{2}.C{l}_{2}$ are solvate isomers. because water is exchanged by chloride ion. This is why both of them show different colours on exposure to sunlight.