Q.Answer the following question.
What is oxidation? Which one of the following pairs of species is in its oxidized state?
a. Mg / Mg²⁺ b. Cu / Cu²⁺ c. O2 / O²⁻ d. Cl2 / Cl⁻

Step 1. Define oxidation. Oxidation is an increase in an element's oxidation number, equivalent to a loss of electrons by that species (Sections 6.1.2 and 6.2.3).

Step 2. Compare pair (a), Mg / Mg²⁺. Mg (free element) is at ON=0; Mg²⁺ is at ON=+2, having lost 2 electrons. Mg²⁺ is the oxidized member of the pair.

Step 3. Compare pair (b), Cu / Cu²⁺. Cu is at ON=0; Cu²⁺ is at ON=+2. Cu²⁺ is the oxidized member.

Step 4. Compare pair (c), O2 / O²⁻. O2 (free element) is at ON=0; O²⁻ is at ON=-2, having GAINED electrons (reduced). So relative to O²⁻, it is O2 that sits at the higher (oxidized) oxidation state.

Step 5. Compare pair (d), Cl2 / Cl⁻. Cl2 is at ON=0; Cl⁻ is at ON=-1 (reduced, having gained an electron). So Cl2 is the oxidized member relative to Cl⁻. …

Comparing the oxidation number of each species within its own pair and picking the higher (more positiv …

• Assuming the FIRST species listed in every pair is always the oxidized one -- in (c) and (d) it is, but the logic is about which ON is higher, not position in the pair. …