Aqueous copper sulphate solution (blue in colour) gives:
$(i)$ a green precipitate with aqueous potassium fluoride,and
$(ii)$ a bright green solution with aqueous potassium chloride
Explain these experimental results.

(N/A) Aqueous $CuSO_4$ exists as $[Cu(H_2O)_4]SO_4$. It is blue in colour due to the presence of $[Cu(H_2O)_4]^{2+}$ ions.
$(i)$ When $KF$ is added:
$[Cu(H_2O)_4]^{2+} + 4F^{-} \to [CuF_4]^{2-} (\text{green precipitate}) + 4H_2O$
$(ii)$ When $KCl$ is added:
$[Cu(H_2O)_4]^{2+} + 4Cl^{-} \to [CuCl_4]^{2-} (\text{bright green solution}) + 4H_2O$
In both these cases,the weak field ligand water is replaced by the $F^{-}$ and $Cl^{-}$ ions,leading to a change in the coordination environment and color.