Question

Mg2+ ion is smaller than O2-ion , although both are isoelectronic .give reason?​

Answer 1

Mg2+ is a cation whereas O2- is an anion.

Cationic radius is always lesser than anionic radius.

Atomic radius ( for neutral atom) is in between cationic and anionic.

So, Cationic R< Atomic R< Anionic R

Answer 2

Its because when Mg loses two electron and form Mg⁺² the electron proton ratio is disturbed and the nucleus attract the reaming electrons with greater force and thus its size decreases.On the other hand,when O gain two electrons the repulsion between electrons increases and O⁻² is larger is size