Which is the odd one out out of aluminum magnesium sodium and silicon?

A couple of different cases could be made here, but the most obvious one is that silicon is the odd element out. The element magnesium is in Group 2, which is the Alkaline Earth metals. Both aluminum and lead are Poor Metals, and silicon is a Metalloid. The operative Word for the first three elements is metal. And silicon is not one. Use the link below to see the really cool Periodic Table posted at Wikipedia. Note that this table is interactive, and each element is a hyperlink to the Wikipedia post on that element. Bookmark this bad boy!