On the basis of position in the electrolchemical series, the metal which does not displace `H_(2)` from water and acid is `:`

Options

A. `Hg`
B. `Al`
C. `Pb`
D. `Ba`

Explanation

To determine which metal does not displace hydrogen from water and acid based on its position in the electrochemical series, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Electrochemical Series**:
The electrochemical series is a list of metals arranged according to their standard electrode potentials. Metals that are higher in the series can displace those that are lower from their compounds.

2. **Identify the Position of Hydrogen**:
Hydrogen has a standard electrode potential (E°) of 0 V. Metals that have a higher reduction potential (more positive E° value) than hydrogen will not displace hydrogen from acids or water.

3. **List the Given Metals**:
The metals provided in the question are:
- Mercury (Hg)
- Aluminum (Al)
- Lead (Pb)
- Barium (Ba)

4. **Check the Standard Electrode Potentials**:
- Mercury (Hg): E° = +0.79 V
- Aluminum (Al): E° = -1.66 V
- Lead (Pb): E° = -0.13 V
- Barium (Ba): E° = -2.90 V

5. **Compare the Electrode Potentials**:
- Mercury has a positive electrode potential (+0.79 V), which is greater than that of hydrogen (0 V).
- All other metals (Al, Pb, Ba) have negative electrode potentials, which means they are below hydrogen in the electrochemical series.

6. **Conclusion**:
Since mercury has a higher reduction potential than hydrogen, it cannot displace hydrogen from acids or water. Therefore, the metal that does not displace hydrogen from water and acid is **Mercury (Hg)**.

### Final Answer:
The metal which does not displace `H₂` from water and acid is **Mercury (Hg)**.

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