(a) When barium chloride solution is added to sodium sulphate solution, then a white precipitate of barium sulphate is formed along with sodium chloride solution:
![](https://www.sarthaks.com/?qa=blob&qa_blobid=6888906337666546078)
Reaction will not take place if the reactants are in a solid state.
(b) When iron nails are dipped in Copper sulphate solution, then Iron sulphate solution and Copper metal are formed.
![](https://www.sarthaks.com/?qa=blob&qa_blobid=11626324913795548988)