The potential associated. with each electrode is known as electrode potential. If the concentration of each species taking part in the electrode reaction is unity (if any gås appears in the electrode reaction, it is confined to 1 atmospheric pressure) and further the reaction is carried out at 298 K, then the potential of each electrode is said to be the standard electrode potential. By convention, the standard electrode potential of hydrogen electrode is 0:0 volt. The electrode potential value for each electrode process is a measure, of relative tendency of the active species in the process to remain in the oxidized / reduced form. A negative `E^@` means that the redox couple is a stronger reducing agent than the `H^(+)//H_2` couple. A positive E mears that the redox couple is a weaker reducing agent than. the `H^(+)//H` couple. The metal with greater positive value of standard reduction potentlal forms the oxide of greater thermal stability:
Which of the following metals will not displace hydrogen from water?

Options

A. Mg
B. Zn
C. Sn
D. Ag

Answer

To determine which of the given metals will not displace hydrogen from water, we need to analyze the standard reduction potentials of each metal and compare them to the standard reduction potential of the hydrogen electrode, which is defined as 0.0 volts.

### Step-by-Step Solution:

1. **Identify the Standard Reduction Potentials**:
- For each metal, we need to find the standard reduction potential (E°) values.
- **Magnesium (Mg)**: E° (Mg²⁺/Mg) = -2.37 V
- **Zinc (Zn)**: E° (Zn²⁺/Zn) = -0.76 V
- **Tin (Sn)**: E° (Sn²⁺/Sn) = -0.14 V
- **Silver (Ag)**: E° (Ag⁺/Ag) = +0.80 V

2. **Understanding Displacement of Hydrogen**:
- The reaction we are considering is:
\[ M + 2H_2O \rightarrow M^{n+} + H_2 + 2OH^- \]
- For a metal (M) to displace hydrogen from water, the oxidation potential of the metal must be greater than that of hydrogen. This means that the standard reduction potential of the metal must be less than 0 V (since E° for H⁺/H₂ is 0 V).

3. **Comparing E° Values**:
- We compare the E° values of the metals with the hydrogen electrode:
- **Mg**: -2.37 V (less than 0, can displace hydrogen)
- **Zn**: -0.76 V (less than 0, can displace hydrogen)
- **Sn**: -0.14 V (less than 0, can displace hydrogen)
- **Ag**: +0.80 V (greater than 0, cannot displace hydrogen)

4. **Conclusion**:
- Since only silver (Ag) has a positive standard reduction potential, it will not displace hydrogen from water. Therefore, the answer is:
- **Silver (Ag)** will not displace hydrogen from water.

### Final Answer:
**Ag (Silver)** will not displace hydrogen from water.