 So metals differ in their activity. A very reactive metal will lose its electrons very easily. A metal loses electrons by definition, so a metal that loses electrons very easily is very reactive. The ions of a metal that are easily reduced, that happens when a metal is not very reactive. So the less reactive a metal, its ions are very easily reduced by gaining electrons. And we end up with these things, these activity series here. So here's a couple of different examples of activity series. This one looks at reactions. This one looks at just oxidation reactions as well. So we've got the oxidation reactions over here. What this means is that metals up here are fairly active, so they give off their electrons easily. So potassium for example is very reactive. Metals down the bottom, let's have a look at silver for example. So silver ions, they reduce relatively easily and that means it's very easy to find silver, well somewhat easy to find silver, as native silver in the environment. Whereas you never find potassium lumps in the dirt. The potassium is very active, so it reacts to the things. Whereas the silver for example, it doesn't react, so it's very easy to find.