The ionic radii (in Å) of N3¯, O2¯ and F¯ are respectively:
1.71, 1.40 and 1.36
N3¯, O2¯ and F¯ are isoelectronic. But due to the difference in their nuclear charges, their ionic radii follow the order N3¯ > O2¯ > F¯. Only option 3 matches this order.