Rank the following elements by atomic radius , na s al ar si

Atomic radius goes as the number of electrons. And there are as many electrons as protons (to have neutral charge).

So if you look up a table and read the atomic number (Z) of each of them, you'll be able to order them. Gotcha? :)

Note that if there were ions: +/- then there would be less or more electrons and things would be more difficult. Probably that is not in your questions.