Question

in above reaction iron nail become brown in colour and the blue colour of copper sulphate solution fades why​

Answer 1

Iron nail becomes brown because there is a layer of sulphate deposited over iron. When iron nail is kept in copper sulphate solution and as iron is more reactive than copper, it displaces copper sulphate from its salt solution becoming iron sulphate .This is known as displacement reaction as a more reactive metal displaces a less reactive metal from its salt solution.