What metals react with aluminium sulphate?
Well, this is a redox-reaction and aluminium is, as aluminium-cations, already in its oxidized state. So we have to look for a reaction in which one of the metals you have listed will “give” its electrons to the aluminium-cations, thus reducing the aluminium-cations to metallic aluminium and getting oxidized itself. To find out, which of the metals you have listed is able to do so, we have to have a look at the Reduction potential of the respective reactions. The reaction Al -> Al3+ + 3e- has one of -1.66 V. For being able to reduce aluminium, the reduction potential of the respective metal has to be lower than the reduction potential of aluminium. Mg -> Mg2+ + 2 e- = -2.36 V Zn -> Zn2+ + 2 e- = -0,76 V Cu -> Cu2+ + 2 e- = +0.35 V As we see, this is only the case for magnesium. Therefore magnesium is the metal you are looking for.