Which of the following metals will not liberate hydrogen when kept in `HCl` solution?

Options

A. Hg
B. Ag
C. Cu
D. All of these

Explanation

To determine which metals will not liberate hydrogen when placed in hydrochloric acid (HCl) solution, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Reaction**: When a metal reacts with an acid like HCl, it typically produces a metal salt and hydrogen gas. The general reaction can be represented as:
\[ \text{Metal} + \text{Acid} \rightarrow \text{Metal Salt} + \text{Hydrogen Gas} \]

2. **Identify the Reactivity Series**: The reactivity series of metals helps us understand which metals can displace hydrogen from acids. Metals that are more reactive than hydrogen will liberate hydrogen gas when they react with acids.

3. **List the Metals**: The metals in question are Zinc (Zn), Mercury (Hg), Silver (Ag), and Copper (Cu).

4. **Analyze Each Metal**:
- **Zinc (Zn)**: Zinc is more reactive than hydrogen, so it will liberate hydrogen when reacted with HCl.
- **Mercury (Hg)**: Mercury is less reactive than hydrogen, so it will not liberate hydrogen when reacted with HCl.
- **Silver (Ag)**: Silver is also less reactive than hydrogen, so it will not liberate hydrogen when reacted with HCl.
- **Copper (Cu)**: Copper is less reactive than hydrogen, so it will not liberate hydrogen when reacted with HCl.

5. **Conclusion**: The metals that will not liberate hydrogen when kept in HCl solution are Mercury (Hg), Silver (Ag), and Copper (Cu).

### Final Answer:
Mercury (Hg), Silver (Ag), and Copper (Cu) will not liberate hydrogen when kept in HCl solution.