A student addd few pieces of aluminium metal to two test tubes A and B containing aqueous solutions of iron sulphate and copper sulphate. In the second part of her experiment, the added iron metal to another test tubes C and D containing aqueous solutions of aluminium sulphate and copper sulphate.
In which test tube or test tubes will she observe colour change? On the basis of this experiment, state which one is the most reactive metal and why ?

Explanation

The chemical reactions involved in all the four tubes are listed.
`"Test tube A : "underset("(Lightgreen)")(3FeSO_(4)(aq))+2Al(s)rarrunderset("(Colourless)")(Al_(2)(SO_(4))_(3)(aq))+3Fe(s)`
`"Test tube B : "underset("(Blue)")(3CuSO_(4)(aq))+2Al(s)rarrunderset("(Colourless)")(Al_(2)(SO_(4))_(3)(aq))+3Cu(s)`
`"Test tube C : "underset("(Colouless)")(Al_(2)(SO_(4))_(3)(aq))+Fe(s)rarrunderset("(No colour change)")("No chemical reaction")`
`"Test tube D : "underset("(Blue)")(Cu(SO_(4))(aq))+Fe(s)rarrunderset("(No colour change)")(FeSO_(4)(s)+Cu(s))`
Change of colour will be observed in test tubes A, B, and D while the solution will remain colourless in test tube C.
On the basis of the chemical reactions, listed above, Aluminium (Al) is the most reactive metal because it has displaced all other metals from their aqueous salt solutions.