Which of the following is displaced by Fe ?

Options

A. (a) Ag
B. (b) Zn
C. (c) Na
D. (d) All of these

Answer

To determine which of the metals can be displaced by iron (Fe), we need to analyze the standard reduction potentials of the metals involved. The displacement reaction occurs when a more reactive metal displaces a less reactive metal from its compound.

### Step-by-Step Solution:

1. **Understanding Displacement Reactions**:
- A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its compound. For example, if we have a compound like AgX and we add a more reactive metal M, it will displace Ag, forming Mx and leaving Ag free.

2. **Identify the Metals**:
- The metals in question are silver (Ag), zinc (Zn), and sodium (Na). We need to check if iron can displace any of these metals.

3. **Standard Reduction Potentials**:
- We need to look up the standard reduction potentials (E°) for the following half-reactions:
- For Fe²⁺ + 2e⁻ → Fe: E° = -0.44 V
- For Ag⁺ + e⁻ → Ag: E° = +0.80 V
- For Zn²⁺ + 2e⁻ → Zn: E° = -0.76 V
- For Na⁺ + e⁻ → Na: E° = -2.71 V

4. **Comparison of Reduction Potentials**:
- To determine if Fe can displace these metals, we compare the reduction potentials:
- **Fe vs. Ag**:
- E°(Fe) = -0.44 V (lower reduction potential than Ag's +0.80 V)
- Since Fe has a lower reduction potential than Ag, Fe can displace Ag.
- **Fe vs. Zn**:
- E°(Zn) = -0.76 V (more negative than Fe's -0.44 V)
- Since Zn has a lower reduction potential than Fe, Fe cannot displace Zn.
- **Fe vs. Na**:
- E°(Na) = -2.71 V (much more negative than Fe's -0.44 V)
- Since Na has a lower reduction potential than Fe, Fe cannot displace Na.

5. **Conclusion**:
- The only metal that can be displaced by iron is silver (Ag). Therefore, the correct answer is **Ag**.

### Final Answer:
- **Silver (Ag)** is displaced by iron (Fe).