At 25°C, which of the following pairs would you predict to react spontaneously? 

Ba²⁺(aq) + 2e^- → Ba(s)                 E° = -2.90 V

Sn⁴⁺(aq) + 2e^- → Sn²⁺(aq)           E° = 0.15 V

Mg²⁺(aq) + 2e^- → Mg(s)               E° = -2.37 V

Zn²⁺(aq) + 2e^- → Zn(s)                 E° = -0.73 V

Na⁺(aq) + e^- → Na(s)                    E° = -2.71 V

Fe³⁺(aq) + 3e^- → Fe(s)                 E° = -0.036 V

Cr³⁺(aq) + 3e^- → Cr(s)                  E° = -0.73 V

Ni²⁺(aq) + 2e^- → Ni(s)                  E° = -0.23 V