Four test tubes were taken and marked A, B, C and D respectively. 2 mL of solution of `Al_(2)(SO)_(3)` in water was filled in each of the four test-tubes. Clean piece of metal zinc was placed in test tube A, clean iron nail was put in test tube B, clean copper wire was placed in test tube C and a clean aluminium wire was placed in test tube D. What colour change would you observe in all the four tubes ?