Definition - What does Activity Series mean?
The activity series is a type of ordering system for elements, which ranks how reactive a certain element is in relation to other elements. The activity series determines the level of reactivity based on how well a certain element can displace hydrogen gas from acidic solutions and water.
The activity series is a very useful tool when selecting materials for a particular application.
Corrosionpedia explains Activity Series
It is important to know which metals are reactive and which are more stable. Referencing the activity series can help ensure that the correct material is selected and that no unwanted reactions occur.
Potassium and lithium are near the top of activity series, which means that they are more likely to react than elements near the bottom of the series. They are also more prone to corrosion. Gold and platinum are near the bottom of the list; their ability to resist reaction is part of the reason they are so valuable.