What special name is given to substances like aluminium oxide.

55 You are given samples of three metals-sodium, magnesium and copper. Suggest any two activities to arrange them in order of their decreasing reactivities. 56 Write one reaction in which aluminium oxide behaves as a basic oxide and another in which it behaves as an acidic oxide. 56 Name another metal oxide which behaves like aluminium oxide. 57 What happens when calcium reacts with water ? Write the chemical equation of the reaction of calcium with water.