atomic radius question?

Question

which ion in each pair has the smaller atomic radius

K- or O2-
Ba2+ or I-
Al3+ or P3-
K+ or Cs-
Fe2+ or Fe3+
F- or S2-

Answer 1

K+(0.133) & O2-(0.140) Hence K+

Ba2+(0.135) & I-(0.216) Hence Ba2+

Al3+(0.050) & P3-(0.212) Hence Al3+

K+(0.133) & Cs+(0.169) Hence K+

Fe2+(0.076) & Fe3+(0.064) Hence Fe3+

F-(0.136) & S2-(0.184) Hence F-.

The figures are in nanometres).

Answer 2

You are actually looking at ionic radii. Since they are charged particles, they are ions.

Heres a helpful table I used when doing ionic radii.
http://en.wikipedia.org/wiki/Ionic_radius

It has the ionic radius of the elements :)
Good luck!