Answer:
The unknown metal could be calcium or magnesium.
Explanation:
Displacement of a metal from its chemical reaction is shown by the reaction known as single displacement reaction. The reactivity of metal is determined by the reactivity series. The metals lying above in the series are more reactive than the metals which lie below in the reactivity series.
Metal B is more reactive than metal A.
The metal which easily displaced aluminium will lie above in the series but that same element cannot displace sodium, so it will lie below in the series.
Hence, from the series, we conclude that the unknown metal could be calcium or magnesium.
