Potassium ions (K^+#) have a positive charge. What happens to a potassium atom's electrons when it becomes an ion?
Well, usually they have caused a reduction in another reagent.
We drop a (small!) chunk of potassium in water, and some of the water is reduced to dihydrogen. And we can represent by a pair of redox rxns:
In a teaching lab, it is better to use lithium or sodium to demonstrate this reaction. Potassium gives a lot of spritz and sparx.........