Arrange `O^(2-),N^(3-) and F^(-)` ions in the decreasing order of their ionic radii and explain the order.

Explanation

The ionic radii of these three ions decrease in the order: `r_(N^(3-)) gt r_(O^(2-)) gt r_(F^(-))`. These ions are isoelectronic and they contain 10 electrons each in their extra-nuclear shell. As the number of protons goes on increasing from `N^(3-)` to `F^(-)` ions, nuclear attractive force for the same number of electrons gradually increases and as a consequence, their ionic radii gradually decrease i.e., their ionic radii follow the above sequence.