Number of electrons based on atomic number and ion charge

Steps:

• Atomic numbers: O = 8, N = 7, Na = 11, Mg = 12.
• Neutral atoms equal atomic number: N has 7 electrons.
• Anions gain electrons: O⁻ = 8 + 1 = 9 electrons.
• Cations lose electrons: Na⁺ = 11 - 1 = 10 electrons; Mg²⁺ = 12 - 2 = 10 electrons.
• Compare values: 9 (A), 7 (B), 10 (C), 10 (D); maximum is 10.

Why C is correct:

• Na⁺ has 10 electrons, the highest number per the definition of ion electron count (atomic number minus positive charge).

Why the others are wrong:

• A. O⁻ has 9 electrons, fewer than 10.
• B. N has 7 electrons, fewer than 10.
• D. Mg²⁺ has 10 electrons, tied with C.

Final answer: C