Half-cell reaction. From the data above , it can be deduced that the most powerful reducing agent of the four metals is

The power of a reducing agent can be determined by its ability to lose electrons and become oxidized. The more easily a metal loses electrons, the stronger the reducing agent it is. To compare the reducing power of Cu, Fe, Ba, and Zn, we can look at their half-cell reactions and standard reduction potentials. The half-cell reaction with the most negative standard reduction potential (E°) is the strongest reducing agent. Looking at the standard reduction potentials: - Cu: Cu²⁺(aq) + 2e⁻ → Cu(s) E° = +0.34 V - Fe: Fe²⁺(aq) + 2e⁻ → Fe(s) E° = -0.44 V - Ba: Ba²⁺(aq) + 2e⁻ → Ba(s) E° = -2.91 V - Zn: Zn²⁺(aq) + 2e⁻ → Zn(s) E° = -0.76 V We can see that Ba has the most negative standard reduction potential, which means it is the strongest reducing agent among the four metals. Therefore, the answer is Ba.