Which term represents the oxidation state concept used to describe electrons in molecules?

• A. Oxidation number
• B. Anode
• C. Electrolyte
• D. Half cell

Answer: (A)

The concept being tested is how we assign electrons in molecules using a bookkeeping value called the oxidation number. This number is assigned to each atom in a molecule or ion to reflect the apparent transfer of electrons, following standard rules (such as elements in their elemental form having zero, oxygen typically −2, hydrogen typically +1, and the sum of all oxidation numbers equaling the overall charge). Tracking these numbers lets us see redox changes: oxidation corresponds to an increase in oxidation number, while reduction corresponds to a decrease. The other terms—anode, electrolyte, and half-cell—refer to parts of an electrochemical setup, not to how we describe electrons in molecules with oxidation numbers.