The series with the correct order of decreasing ionic size for the ions is
1
\(\text{O}^{2-} > \text{F}^- > \text{Na}^+ > \text{Mg}^{2+}\)
2
\(\text{F}^- > \text{O}^{2-} > \text{Na}^+ > \text{Mg}^{2+}\)
3
\(\text{Na}^+ > \text{F}^- > \text{O}^{2-} > \text{Mg}^{2+}\)
4
\(\text{Mg}^{2+} > \text{Na}^+ > \text{O}^{2-} > \text{F}^-\)