The charges of a set of isoelectronic ions vary from 3 + to 3-. Place the ions in order of increasing size.

Iso-electronic species have same number of electrons. Positive charged ions will have smaller size. As electrons add, size increases due to electronic repulsion.

Following species are isoelectronic.

Al³⁺ < Mg²⁺ < Na¹⁺ < Ne < F⁻¹ < O⁻² < N⁻³