For each of the following sets of atoms and ions, arrange the members in order of increasing size.

Question

Mg2+ F- and Na+

Answer 1

It is somewhat like this as a trend:

Metal ions get smaller as you go to the right on the periodic table, and non-metals get larger.

Now, those are trends. In this case, look at the actual sizes.
http://www.chemguide.co.uk/atoms/properties/atradius.html

Answer 2

thanks:)