An oxidation number describes how many electrons an atom gains, loses, or shares to become stable.

• A. Atomic mass
• B. Valence
• C. Oxidation number
• D. Charge

Answer: (C)

Oxidation numbers are a bookkeeping tool chemists use to track electrons in bonding and reactions. They indicate how many electrons an atom would gain, lose, or have assigned to it to reach a more stable, often eight-electron, arrangement. This framing is exactly what the statement is capturing: the oxidation number is a numeric way to represent how electrons are redistributed to move toward stability, rather than the atom’s actual physical charge in every situation. Remember that oxidation numbers can be positive, negative, or zero and may not match the real charge on an atom in covalent molecules, though they do align with ionic charges in ions. For example, in water, oxygen is assigned an oxidation number of -2 and each hydrogen is +1, summing to zero for the molecule. In contrast, atomic mass measures how heavy an atom is, and valence refers to bonding capacity, not the bookkeeping of electron transfer. Charge is the actual net electric charge of a species, which oxidation numbers formalize rather than always equal.