The first, second and third ionisation energies (E1,E2 & E3) for an element are 7eV, 12.5 eV and 42.5 eV respectively. The most stable oxidation state of the element will be :

A large difference between second and third ionisation energies of the element. Element is having 2 valence electrons. So most stable oridation state of the element will be +2.