Which of the following metals will react spontaneously with NiCl_2(aq)?

• A. Zn
• B. Ag
• C. Pb
• D. Cu

Answer: (A)

Verified step by step guidance

1. Understand that a metal will react spontaneously with a metal salt solution if it is more reactive (has a higher tendency to lose electrons) than the metal ion in the solution. This is determined by comparing their standard reduction potentials.
2. Identify the metal ion in the solution: NiCl_2 contains Ni^{2+} ions. We need to consider the standard reduction potential for the half-reaction: \(\mathrm{Ni^{2+} + 2e^- \rightarrow Ni}\).
3. Look up the standard reduction potentials (\(E^\circ\)) for the metals involved: Zn, Ag, Pb, Cu, and Ni. Metals with a more negative reduction potential than Ni will tend to oxidize (lose electrons) and thus react spontaneously with Ni^{2+}.
4. Compare the reduction potentials: if the metal's \(E^\circ\) is lower (more negative) than that of Ni^{2+}\(, the metal will be oxidized, reducing Ni^{2+}\) to Ni metal, and the reaction will be spontaneous.
5. Based on this comparison, select the metal(s) that have a more negative standard reduction potential than Ni^{2+} to determine which will react spontaneously with NiCl_2(aq).