Which of the following elements is most likely to form a -3 ion?

• A. O (Oxygen)
• B. N (Nitrogen)
• C. Mg (Magnesium)
• D. Na (Sodium)

Answer: (B)

Verified step by step guidance

1. Understand that the charge on an ion is related to how many electrons an atom gains or loses to achieve a full outer electron shell, often resembling the nearest noble gas configuration.
2. Recall that elements tend to gain or lose electrons to complete their valence shell, with nonmetals typically gaining electrons to form negative ions (anions) and metals typically losing electrons to form positive ions (cations).
3. Look at the given elements: Oxygen (O), Nitrogen (N), Magnesium (Mg), and Sodium (Na). Identify their group numbers in the periodic table to determine their typical ionic charges. Oxygen and Nitrogen are nonmetals, while Magnesium and Sodium are metals.
4. Nitrogen is in group 15 (or 5A), meaning it has 5 valence electrons and needs to gain 3 electrons to complete its octet, making it likely to form a -3 ion (N³⁻). Oxygen, in group 16 (6A), typically gains 2 electrons to form a -2 ion (O²⁻). Magnesium and Sodium, being metals, tend to lose electrons and form positive ions (Mg²⁺ and Na⁺ respectively).
5. Therefore, the element most likely to form a -3 ion is Nitrogen because it gains three electrons to complete its valence shell.