Based on the given standard electrode potential values, arrange Mg, Cu and Ni in increasing reactivity. Explain how electrode potential relates to metal reactivity. Mg²⁺ + 2e⁻ → Mg E° = −2.37; Cu²⁺ + 2e⁻ → Cu E° = +0.34; Ni²⁺ + 2e⁻ → Ni E° = −0.25.