Which atom is most likely to form an ion with a +2 charge?

Name: Which atom is most likely to form an ion with a +2 charge?
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Question

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Calcium (#20) only has two valence electrons, making it more likely to give up these two electrons to form a stable cation with a +2 charge. Scandium (#21) and aluminum (#13) both have three valence electrons and can form cations with a +3 charge. Oxygen (#8) and fluorine (#9) are highly electronegative and tend to gain electrons to form anions with a -2 charge.

Which Atom Is Most Likely to Form an Ion with a +2