Magnesium loses electrons successively to form `Mg^(+),Mg^(2+)andMg^(3+)` ions . Which step will have the highest ionisation energy and why ?

Explanation

`Mg toMg^(+)+e(l.E_(1)=X_(1))` Neutral atom
`Mg^(+)tomg2++e-(l.E_(3)=X_(2))` unipositive atom
`Mg^(2+)toMg^(3+)+e^(-)(l.E_(3)=X_(3))` Dipositive cation
(i) The third step will have the highest Ionization energy `lE_(3)gti.E_(2)gtl.E_(1)`
(ii) Because from neutral gaseous atom , the electron removal is easy and less amount of energy is required . But from a dipositive cation , there will be more number of protons than the electrons and more is more forces of attraction between the nucleus and electron . So ,the removal of electron in a dipositive cation , becomes highly difficult and more energy is required.