Section 2 f) Summary

Metals can be placed in an order of most to least reactive, called the reactivity series.

This can be remembered using an acronym:
Please
Stop
Calling
Me
A
Cranky
Zebra
I
Teach
Lions
How
Cars
Save
Gold
Printers

More reactive metals will displace less reactive ones in a compound (e.g. a metal salt or a metal oxide), which can be demonstrated by dissolving the compound in water to make it aqueous, then adding another metal to see if it reacts; if it does, then it is more reactive. If it doesn't, it's less reactive.
Reactivity series can also be determined by evaluating the intensity of reaction with water or acid.

Sacrificial protection
Iron is a useful metal, and it's on the less reactive side. But, when exposed to water and air, it will rust. It can be protected using grease, oil, paint or plastic, but another method is galvanising.
Galvanising is a form of sacrificial protection, wherein the iron is coated in a layer of zinc, which is a more reactive metal. This causes the oxygen and water to react with the zinc instead of the iron, protecting it. This method can be employed in different metals, but is called sacrificial protection and not galvanising in this case.