Which one of the following elements is most likely to gain electrons when forming an ion?

• A. Mg
• B. Na
• C. Al
• D. Cl

Answer: (D)

Verified step by step guidance

1. Understand that elements that tend to gain electrons to form ions are typically nonmetals, which have higher electronegativities and are closer to completing their valence electron shells.
2. Recall that metals like Mg (magnesium), Na (sodium), and Al (aluminum) usually lose electrons to form cations because they have relatively low electronegativities and fewer valence electrons to lose.
3. Recognize that chlorine (Cl) is a nonmetal with seven valence electrons, so it tends to gain one electron to complete its octet and form an anion (Cl⁻).
4. Compare the position of each element in the periodic table: Mg, Na, and Al are metals in groups 2, 1, and 13 respectively, while Cl is a halogen in group 17, known for gaining electrons.
5. Conclude that Cl is most likely to gain electrons when forming an ion, unlike the metals listed, which typically lose electrons.