In sodium chloride, what are the oxidation numbers of sodium and chlorine?

• A. Na +1, Cl -1
• B. Na -1, Cl +1
• C. Na 0, Cl 0
• D. Na +2, Cl -2

Answer: (A)

Oxidation numbers in compounds reflect how electrons are distributed between atoms. In an ionic salt like sodium chloride, the metal tends to lose electrons to form a positive ion, while the non-metal tends to gain electrons to form a negative ion. Sodium, an alkali metal, loses one electron to achieve a stable electron configuration, giving Na+ with an oxidation number of +1. Chlorine, a halogen, gains one electron to complete its octet, producing Cl− with an oxidation number of −1. The compound is neutral overall, so the charges balance: +1 plus −1 equals zero. Other suggested options would imply unusual or inconsistent charges for these elements in this compound, which doesn’t fit how these elements typically behave. Thus, the oxidation numbers are Na +1 and Cl −1.