Which of the following is true? a. 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. b. cesium is the most active group 1 metal, because its valence electron is held more tightly than the others in the same group. c. group 1 elements are more reactive than the group 2 elements because they have more valence electrons to lose. d. the least reactive element in group 2 is the one with the largest atomic radium and the least amount of attraction between the nucleus