Final answer:
The least reactive elements are found in Group 8 of the periodic table, known as the noble gases. These include Helium, Neon, Argon, Krypton, Xenon, and Radon, with Helium being the least reactive due to its full valence electron shell.
Step-by-step explanation:
Least Reactive Element
When considering the reactivity of elements, noble gases in Group 8 of the periodic table are known for their lack of reactivity. Among the noble gases, Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn) are extremely unreactive due to their full valence electron shells. Consequently, they do not readily form compounds with other elements. Based on this distinguished characteristic of noble gases, it is reasonable to infer that one of these elements would be considered the least reactive.
In contrast, elements like Rb (Rubidium) have low first ionization energy and are very reactive, making them inappropriate choices for the least reactive element. Likewise, elements in Group 1 (alkali metals) and Group 2 (alkaline earth metals) are also quite reactive, further emphasizing the non-reactive nature of noble gases.
Therefore, when asked to identify the least reactive element, one should select an element from Group 8, with Helium being the top candidate due to its role as the first element in the noble gas series.