Which metal can be oxidized by a Pb^{2+} solution but not by a Cd^{2+} solution?

• A. Cu
• B. Ag
• C. Fe
• D. Zn

Answer: (D)

Verified step by step guidance

1. Understand the problem: We need to find a metal that can be oxidized by Pb^{2+} ions but not by Cd^{2+} ions. Oxidation here means the metal loses electrons and the metal ions in solution gain electrons (are reduced).
2. Recall that whether a metal can be oxidized by a metal ion solution depends on their relative standard reduction potentials. The metal ion with a higher reduction potential will be reduced, causing the other metal to be oxidized.
3. Look up the standard reduction potentials (E^{\circ}) for the relevant half-reactions: Pb^{2+} + 2e^{-} \rightarrow Pb, Cd^{2+} + 2e^{-} \rightarrow Cd, and the oxidation half-reactions for the metals Cu, Ag, Fe, and Zn.
4. Compare the reduction potentials: For a metal M to be oxidized by Pb^{2+}, the E^{\circ} of Pb^{2+}/Pb must be higher than that of M^{n+}/M, so Pb^{2+} can be reduced while M is oxidized. For the same metal M not to be oxidized by Cd^{2+}, the E^{\circ} of Cd^{2+}/Cd must be lower than that of M^{n+}/M.
5. Identify the metal that fits these criteria by comparing the values: it should have a standard reduction potential lower than Pb^{2+}/Pb but higher than Cd^{2+}/Cd, meaning Pb^{2+} can oxidize it but Cd^{2+} cannot.