Why does strontium form plus 2 ion?

Strontium forms a plus 2 ion (Sr²⁺) because it has two valence electrons in its outermost shell (the 5s orbital). By losing these two electrons, strontium achieves a more stable electron configuration, resembling that of the noble gas krypton. This loss of electrons allows strontium to attain a full outer shell, which is energetically favorable and leads to the formation of the Sr²⁺ ion.