AP and TS EAMCET Engineering 2020 Model Paper 1

On increasing atomic number of isoelectric species ionic radii decreases due to increasing effective nuclear charge (Zeff).
Radius∝

1

Zeff

So, as the negative charge increases ionic radii increases while on increasing positive charge ionic radii decreases. Anions having higher ionic radii than the cation.
Hence, order of radii
O2−>F−>Na+>Mg2+>Al3+