posted by maria .
Which ion has larger radius O2- or F 1-?why?
F^- is smaller because the nuclear charge is nigher (by 9 vs 8) and the larger + charge is attracting the electrons that are in the same orbit as oxygen; therefore the outside shell is pulled a little stronger.
don't they both have 10 electrons.
does that mean they both have same radius
Yes, both have 10 electrons.
O has 8 protons pulling on those 10 electrons but F has 9 protons pulling on ten electrons. The 9+ charges will pull those 10 electrons in a little more than the 8 protons will; therefore, F^- will be smaller.