Answer:
Neon (Ne)
Step-by-step explanation:
Different groups on the periodic table have different reactivities.
Periodic Table Groups
On the periodic table, vertical columns are referred to as groups or families. Elements in groups have the same number of valence electrons. The number of valence electrons helps determine the reactivity of an element. If an element has a full valence electron shell, then it will be highly unreactive. So, groups that have the highest number of valence electrons will be the least reactive.
Halogens
The right-most group on the periodic table is known as the halogen group. All of the elements in this group have 8 valence electrons (except helium, which only has 2). All halogens have a full valence shell. This makes halogens the least reactive group. By looking at the periodic table, we can see that neon is a halogen; thus it is a part of the least reactive group of elements.