Storing reactive metals
The first use of the activity series is in identifying the measures to be taken to keep metals safe when they are stored.
The problem and the answer
Highly reactive metals such as sodium (Na), potassium (K) and calcium (Ca) react with the constituents of the air if they are left exposed to it.
The solution
Such metals must therefore be stored in liquids such as kerosene or liquid paraffin.
Why that works
Kerosene and paraffin keep the metal away from the air and from water vapour. They also do not react with these metals — so the metal stays safe.
Why not store them under water?
Water is also a liquid that keeps out the air. But we saw in activity 16.4 that sodium reacts rapidly with water itself — so storing it under water would make matters very much worse.
Position in the series fixes the storage method
Top (K, Na, Ca) — must be kept immersed in a liquid.
Middle (Mg, Al, Zn, Fe) — a dry place is enough.
Bottom (Ag, Pt, Au) — no special protection needed.