Which of the following is true?

A. The least reactive element in group 2 is the one with the largest atomic radium and the least amount of attraction between the nucleus and the valence electrons.
B. Group 1 elements are more reactive than the group 2 elements because they have more valence electrons to lose.
C. Cesium is the most active group 1 metal, because its valence electron is held more tightly than the others in the same group.
D. Lithium is the least reactive element in group 1, because it is the smallest and holds its valence electron more tightly than the others in the same group.

D. Lithium is the least reactive element in group 1, because it is the smallest and holds its valence electron more tightly than the others in the same group.

Explanation:

Lithium is at the top of group one and has only two energy levels. It has the smallest atomic radius of all the elements in group one. This means it's valence electron is the closest one to the nucleus of all the group 1 elements. The nucleus holds this electron more tightly than other group 1 nuclei which is why lithium is the least reactive of all the group 1 metals.