What does displacement reaction tell you about the reactivity of the 2 metals involved?

it tells me that one element is more reactive than the other

Explanation:

using the reactivity series. the element that come above is the most reactive e.g

potassium

sodium

calcium

magnesium

potassium is more reactive than sodium and the following below

calcium is more reactive than magnesium since it is below it in the reactivity series.

CONCLUSION, reactivity decreases down the reactivity series and increases up the reactivity series. the example i gave is part of the reactivity series of cations but there is also for anions