The group with the greatest metallic character on the periodic table is Group 1, which consists of the alkali metals such as lithium, sodium, potassium, and so on. These metals are highly reactive and tend to lose their outermost electron easily, which is a characteristic of metallic behavior.
On the other hand, the group with the lowest metallic character is Group 18, which contains the noble gases like helium, neon, argon, etc. These elements are characterized by their complete valence electron shells, meaning they do not tend to lose or gain electrons, thus exhibiting non-metallic properties.
In summary, as you move from left to right across the periodic table, the metallic character decreases, while it increases as you move from top to bottom within a group. Therefore, alkali metals in Group 1 are the most metallic, and noble gases in Group 18 are the least metallic.