Question

why does the blue colour of copper sulphate change when a piece of iron is dropped into it

Answer 1

copper sulphate formula is cuso4
and after reacting with fe (iron)
it converts into feso4+cu and colour is changed

Answer 2

"When iron nails is dipped in copper sulphate solution,the colour of the solution becomes blue due to formation of iron sulphate..."
Fe+Cu So4=Fe So4+Cu
Blue. =. Green