Which of the following species is the best reducing agent?

• A. Cl_2(g)
• B. Zn(s)
• C. Cu^{2+}(aq)
• D. Fe^{3+}(aq)

Answer: (B)

Verified step by step guidance

1. Understand that a reducing agent is a species that donates electrons and gets oxidized in a redox reaction.
2. Recall that the best reducing agent is the species that has the greatest tendency to lose electrons (i.e., it is easily oxidized).
3. Look at the given species: Cl_2(g), Zn(s), Cu^{2+}(aq), and Fe^{3+}(aq). Among these, Zn(s) is a solid metal, while the others are either nonmetals or ions in solution.
4. Consider standard reduction potentials: species with lower (more negative) reduction potentials are better reducing agents because they more readily lose electrons.
5. Since Zn(s) has a more negative standard reduction potential compared to the other species, it is the best reducing agent among the options.