na+ has only three shell has one valence electron which it will loose to be reactive where as in k+ the no of shells are 5 so electrons are having less attraction from the nucleus than that in sodium(na),so Na is less reactive than k. read more
Sodium and potassium belongs to same group . Both has 1 electron to donate but sodium is less reactive because nuclear attraction makes it little bit difficult to loose electron as compared to potassium in which nuclear attraction becomes unable to pull the electrons towards itself . read more
The atomic radius of potassium is greater than that of sodium. Therefore, the single valence electron that exists for all alkali metals is located farther from the nucleus for potassium than sodium. This results in less energy required to remove that valence electron from potassium than from sodium, leading to increased reactivity. read more
Potassium is in the most reactive group of elements, the alkali metals, but it's not the most reactive metal within the group. The alkali metals, Group 1A, are the most reactive metals because they have one valence or outer electron. read more