Here's why:
* Alkali Metals: All three elements (Cs, Rb, and Na) belong to Group 1 of the periodic table, known as the alkali metals. These elements are highly reactive due to their single valence electron, which they readily lose to form positive ions.
* Reactivity Trend: Reactivity within the alkali metals increases as you move down the group. This means Cesium (Cs) is the most reactive, followed by Rubidium (Rb), and then Sodium (Na).
Therefore, sodium (Na) is the least reactive out of the three.
