Here's why:
* They are both in the same group (Group 1, Alkali metals) of the periodic table. This means they have the same number of valence electrons (1) and therefore similar chemical properties.
* They readily form +1 ions. Both sodium and potassium lose one electron to achieve a stable electron configuration.
* They are highly reactive metals. They react vigorously with water and air, releasing hydrogen gas.
While other elements in Group 1 will also have similar properties to sodium, potassium is the closest in terms of reactivity and behavior.
