2.31 deduce the position of a metal within the reactivity series using displacement reactions between metals and their oxides, and between metals and their salts in aqueous solutions

If you set up an experiment with a  metal oxide or a metal salt 

dissolved in water

introduce a more reactive metal and it will displace the current one

introduce a less reactive metal and no displacement will take place

From this you can deduce which metals are more and less reactive.