Correct option is (b) copper sulphate solution reacts with K4[Fe(CN)6]
The blue colouration is due to the formation of a complex compound. The complex compound is formed by the combination of a metal ion with a ligand. The ligand is a molecule or ion that can donate a pair of electrons to the metal ion to form a coordinate bond.
a) Ammonium hydroxide dissolves in copper sulphate: When ammonium hydroxide is added to copper sulphate, a light blue precipitate of copper hydroxide is formed. The blue colouration is not obtained in this reaction because copper hydroxide is not a complex compound.
b) Copper sulphate solution reacts with K4[Fe(CN)6]: When copper sulphate solution is added to potassium ferrocyanide solution, a brown precipitate of copper ferrocyanide is formed. The blue colouration is obtained in this reaction because copper ferrocyanide is a complex compound.
c) Ferric chloride reacts with sod. ferrocyanide: When ferric chloride is added to sodium ferrocyanide solution, a dark blue precipitate of iron ferrocyanide is formed. The blue colouration is obtained in this reaction because iron ferrocyanide is a complex compound.
d) Anhydrous CuSO4 is dissolved in water: When anhydrous copper sulphate is dissolved in water, a white crystalline solid of copper sulphate pentahydrate is formed. The blue colouration is not obtained in this reaction because copper sulphate pentahydrate is not a complex compound.
Therefore, the correct option is Copper sulphate solution reacts with K4[Fe(CN)6].
