Octet Rule in Ion Formation Steps: - Sodium (atomic number 11) loses one electron to form Na⁺, resulting in 10 electrons and a neon-like configuration with a full outer shell of 8 electrons. - Chlorine (atomic number 17) gains one electron to form Cl⁻, resulting in 18 electrons and an argon-like configuration with a full outer shell of 8 electrons. - Both ions achieve stability through the octet rule, sharing this electron arrangement. - This common property distinguishes them from neutral atoms or other ions. Why B is correct: - Na⁺ and Cl⁻ both follow the octet rule, attaining eight valence electrons for chemical stability, as defined in ionic bonding theory. Why the others are wrong: - A: Neutral Na atoms have equal protons (11) and neutrons (12 in common isotope), while Cl atoms vary; not true for all and irrelevant to ions. - C: Na⁺ dissolves in water; Cl⁻ forms soluble salts; neither "sinks" as ions. - D: In molten NaCl electrolysis, Na⁺ deposits at the negative cathode, while Cl⁻ forms Cl₂ gas at the positive anode. Final answer: …