Aqueous copper sulphate solution (blue) gives - (1) a green precipitate with aqueous potassium fluoride

Explanation

Aqueous copper sulphate contains coordination entity `[Cu(H_(2)O)_(4)]^(2+)`, which is blue in colour.
(1) On addition of aqueous KF solution, `H_(2)O` ligands are replaced by `F^(-)` ligands forming a green precipitate of the coordination compound `K_(2)[CuF_(4)]`
`[Cu(H_(2)O)_(4)]^(2+)+underset("potassium tetrafluorocuprate (II) (green)")(4KF rarr K_(2)[CuF_(4)]darr+2K^(+)+4H_(2)O)`