The arrangement of metals in a vertical column in the decreasing order of their reactivities is called the reactivity series or activity series of metals. The most reactive metal is at the top position of the reactivity series. The least reactive metal is at the bottom of the reactivity series.
Hydrogen, though a non-metal, has been included in the activity series of metals only for comparison. Apart from it, the hydrogen atom also has tendency to lose its valence electron and form cation like the behaviour shown by metals. Thus,
`H to H^(+) + e^(-)`
An element 'X' after reacting with acids liberate hydrogen gas and can displace lead and tin from their salt solution. The metal 'X' is

Options

A. copper
B. gold
C. nickel
D. hydrogen.

Explanation

To determine the metal 'X' that reacts with acids to liberate hydrogen gas and can displace lead and tin from their salt solutions, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Reactivity Series**: The reactivity series is a list of metals arranged in order of decreasing reactivity. The most reactive metals are at the top, and the least reactive metals are at the bottom. Hydrogen is included in this series for comparison.

2. **Identify the Position of Hydrogen**: In the reactivity series, metals that are above hydrogen can displace hydrogen from acids and can also displace metals that are below them in the series.

3. **Analyze the Given Conditions**: The problem states that the metal 'X' liberates hydrogen gas when reacting with acids. This indicates that metal 'X' must be more reactive than hydrogen.

4. **Displacement of Lead and Tin**: The metal 'X' can also displace lead (Pb) and tin (Sn) from their salt solutions. This means that 'X' must be more reactive than both lead and tin.

5. **Check the Reactivity of Common Metals**:
- Metals like copper (Cu), silver (Ag), and gold (Au) are less reactive than hydrogen and cannot displace it.
- Metals like zinc (Zn), iron (Fe), and nickel (Ni) are more reactive than hydrogen and can displace it.

6. **Determine the Most Suitable Metal**:
- Among the more reactive metals, we need to check which one can displace lead and tin.
- Nickel (Ni) is more reactive than hydrogen and can displace both lead and tin from their salt solutions.

7. **Conclusion**: Based on the analysis, the metal 'X' is **Nickel (Ni)**.

### Final Answer:
The metal 'X' is Nickel (Ni).

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