# Question #677b8

Calcium is an $\text{alkaline earth}$; it comes from Group 2 of the Periodic Table.
Sodium is a Group 1 alkali metal, which are very reactive species. The question should have compared the reactivity of sodium towards potassium. Potassium, $Z = 19$, is much more reactive than sodium metal, $Z = 11$. The valence electron of potassium is much further removed from the nuclear core, with the result that potassium metal is a much better reductant. The difference in reactivity between the two metals reflect this.