Among the elements listed (Li, Be, Mg, Na), sodium (Na) has the least metallic character.
Metallic character generally increases down a group in the periodic table and decreases across a period from left to right. In this case, lithium (Li) and sodium (Na) are both alkali metals, with sodium being lower in the group and thus more metallic. Beryllium (Be) and magnesium (Mg) are alkaline earth metals, and they are more metallic compared to lithium and sodium due to their position in the periodic table.
In terms of metallic character in this subset, sodium has a higher metallic character than lithium, beryllium, and magnesium, making the least metallic character belong to beryllium (Be). Therefore, beryllium (Be) has the least metallic character.