Final answer:
The noble gases in group 18 of the periodic table represent the least reactive column of elements due to their full valence electron shells, which render them stable and minimally reactive.
Step-by-step explanation:
The least reactive column of elements in the periodic table is the noble gases, which are found in group 18. These elements, including helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), are known for their lack of reactivity due to their full valence electron shells, making them very stable and unlikely to form chemical bonds under normal conditions. Unlike the alkali metals in group 1 or the halogens in group 17, which are highly reactive, the noble gases rarely participate in chemical reactions and don't naturally form compounds with other elements.
In contrast, the elements in group 1 of the periodic table, which includes alkali metals like lithium (Li), sodium (Na), and potassium (K), are the most reactive among metals and react vigorously with substances like water. Similarly, the halogens in group 17 are also highly reactive and readily form compounds by accepting electrons during chemical reactions. However, the reactivity of group 2, the alkaline earth metals, is less than that of the alkali metals as they need to remove two electrons for reactions.