Step 1: Understanding the Concept:
This question deals with the relative reactivity of metals based on their standard electrode potentials (E$^\circ$). A more negative E$^\circ$ indicates a stronger reducing agent (more easily oxidized). A more positive E$^\circ$ indicates a stronger oxidizing agent (more easily reduced). A spontaneous redox reaction occurs when a stronger reducing agent reacts with a stronger oxidizing agent.
Step 2: Key Formula or Approach:
The rules for predicting spontaneity are:
- A species can reduce another species if its E$^\circ$ is more negative (lower) than the other's.
- A species can oxidize another species if its E$^\circ$ is more positive (higher) than the other's.
- In other words, a metal can displace (reduce the ion of) any metal below it in the electrochemical series (i.e., any metal with a more positive E$^\circ$).
Step 3: Detailed Explanation:
Let's list the given standard reduction potentials:
- $E^\circ(Zn^{2+}/Zn) = -0.76$ V
- $E^\circ(Cu^{2+}/Cu) = +0.34$ V
- $E^\circ(Ag^{+}/Ag) = +0.80$ V
The order of reducing strength of the metals (ability to get oxidized) is the reverse of their E$^\circ$ values:
\[ \text{Zn}>\text{Cu}>\text{Ag} \]
The order of oxidizing strength of the ions (ability to get reduced) is the same as their E$^\circ$ values:
\[ Ag^+>Cu^{2+}>Zn^{2+} \]
Now let's evaluate each statement:
- (A) Ag can oxidize Zn and Cu: This is incorrect. Ag is the weakest reducing agent (least easily oxidized). It is the ions, Ag$^+$, that are strong oxidizing agents.
- (B) Ag can reduce Zn$^{2+$ and Cu$^{2+}$:} This is incorrect. Ag metal is a weaker reducing agent than both Zn and Cu. It cannot reduce their ions. The reactions $Ag + Zn^{2+} \rightarrow$ and $Ag + Cu^{2+} \rightarrow$ are non-spontaneous.
- (C) Zn can reduce Ag$^{+$ and Cu$^{2+}$:} This is correct. Zn is the strongest reducing agent among the three. It is more reactive than both Cu and Ag, so it can displace them from their salt solutions. The reactions $Zn + 2Ag^+ \rightarrow Zn^{2+} + 2Ag$ and $Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$ are both spontaneous.
- (D) Cu can oxidize Zn and Ag: This is incorrect. Cu metal is a reducing agent. It cannot oxidize other metals. Cu$^{2+}$ ions can oxidize Zn, but not Ag.
Step 4: Final Answer:
The correct statement is that Zn can reduce Ag$^{+}$ and Cu$^{2+}$. Therefore, option (C) is correct.