For `Na^(+),Mg^(2+),F^(-) and O^(2-)`, the correct order of increasing ionic radii is :

Explanation

`Mg^(2+) lt Na^(+) lt F^(-) lt O^(2-)`
This order can be justified on the basis of the fact that a negative anion is larger than its neutral atom due to a decrease in effective nuclear charge. As the valence electrons now experience weaker attractions from the nucleus, its size must be largest. On the contrary, a cation will have smaller size than its neutral atom due to an increase in effective nuclear charge. Higher the positive charge, smaller the cation.