What is the oxidation half-reaction for 2{Mg} + {O}₂ → 2{MgO}?
a. 2O²⁻ → {O}₂ + 4e⁻
b. {Mg}²⁺ + 2e⁻ → {Mg}
c. {Mg} → {Mg}²⁺ + 2e⁻
d. {O}₂ + 4e⁻ → 2{O}₂⁻