Of the elements below, is the least metallic. na mg al p ar

last option: Ar

Justification:

The metallic character of the elements in the periodic table increase from right to left and from top to bottom.

That means that the elements of groups (rows) 1 and 2 and periods (columns) 6 and 7 are the most metallics, and the elements of groups 17 and 18 and periods 1 and 2 are the least metallics.

Na, Mg, Al, P and Ar are in the same period (row) so you can differentiate their metallic character by the rule that  the more to the right on the row the less metallic the element is.

Na (left end the row) is the most metallic and Ar (right end of the row)  is the least metallic.

P and Ar are less metallic.

Then, the list arranged in order of decreasing metallic character is:

Na > Mg > Al > P > Ar.

Therefore, the answser is Ar.