The Correct Order of Radii is

The correct order of radii is F−<O2−<N3−. The size of isoelectronic falls with rising atomic number. In isoelectronic species,
Ionic radii are ∝1Z
Since F−,O2− and N3− have the exact number of electrons, so the order of ionic radii is: F−<O2−<N3−
The general periodic trend of the atomic radii falls from left to right in a period and rises down the group.