Question

An iron knife kept dipped in a copper sulphate solution turn the blue solution light green. Why

Answer 1

An iron knife kept dipped in a copper sulphate solution turn blue solution light green when the iron absorbs the properties of copper then it turns solution from blue to green.

Answer 2

Because the iron from the knife displaces the copper from the solution (as iron is more reactive than copper )and forms iron sulphate solution which is green in colour. When an iron knife is dipped is copper sulphate solution, after some time we'll see it has turned light green (from blue) in colour.