Final answer:
The element in the 3rd period most likely to form a +2 ion is Magnesium (Mg), because, as a Group 2 element, it tends to lose two electrons.
Step-by-step explanation:
Based on the periodic table, the element in the 3rd period that is most likely to form an ion with a +2 charge is Magnesium (Mg). This element belongs to Group 2 (or IIA), where elements tend to lose two electrons to achieve a full outermost energy level, thereby acquiring a +2 charge.
Examples of compounds that illustrate this are magnesium oxide (MgO) and magnesium chloride (MgCl2). In both of these compounds, magnesium has lost two electrons and consequently carries a charge of +2.
Learn more about 3rd period elements