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^(-)`
The metal which does not liberate hydrogen gas after reacting with acid is

Options

A. zinc
B. lead
C. tin
D. gold.

Answer

To determine which metal does not liberate hydrogen gas after reacting with acid, we will refer to the reactivity series of metals. Here’s a step-by-step solution:

### Step 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, while the least reactive metals are at the bottom. Metals that are above hydrogen in the series can displace hydrogen from acids, while those below hydrogen cannot.

### Step 2: Identify the Position of Metals
From the reactivity series, we have the following arrangement:
1. Potassium (K)
2. Sodium (Na)
3. Aluminum (Al)
4. Zinc (Zn)
5. Iron (Fe)
6. Lead (Pb)
7. Hydrogen (H)
8. Copper (Cu)
9. Silver (Ag)
10. Gold (Au)

### Step 3: Analyze the Question
The question asks for a metal that does not liberate hydrogen gas when reacting with an acid. This means we need to identify a metal that is positioned below hydrogen in the reactivity series.

### Step 4: Identify Metals Below Hydrogen
From the list, we can see that:
- Copper (Cu), Silver (Ag), and Gold (Au) are all below hydrogen in the reactivity series.

### Step 5: Conclusion
Among the metals listed, Copper (Cu), Silver (Ag), and Gold (Au) will not liberate hydrogen gas when reacting with acids. However, if we are to select one, Gold (Au) is often highlighted as the least reactive and is commonly referenced in this context.

### Final Answer
The metal which does not liberate hydrogen gas after reacting with acid is **Gold (Au)**.

---