When treated with nitric acid which of the following liberates hydrogen ?

Options

A. Zinc
B. Copper
C. Magnesium
D. Mercury

Explanation

To determine which of the given metals liberates hydrogen when treated with nitric acid (HNO3), we can follow these steps:

### Step 1: Understand the Reaction
When a metal reacts with nitric acid, it typically forms a metal nitrate and may liberate hydrogen gas. The general reaction can be represented as:
\[ \text{Metal} + \text{HNO}_3 \rightarrow \text{Metal Nitrate} + \text{H}_2 \]

### Step 2: Identify the Reactivity of Metals
For a metal to liberate hydrogen from an acid, it must be more reactive than hydrogen. The reactivity series indicates that metals like zinc (Zn) and magnesium (Mg) are more reactive than hydrogen, while copper (Cu) and mercury (Hg) are less reactive.

### Step 3: Analyze Each Metal
- **Zinc (Zn)**: More reactive than hydrogen, can potentially liberate hydrogen.
- **Copper (Cu)**: Less reactive than hydrogen, will not liberate hydrogen.
- **Magnesium (Mg)**: More reactive than hydrogen, can potentially liberate hydrogen.
- **Mercury (Hg)**: Less reactive than hydrogen, will not liberate hydrogen.

### Step 4: Consider the Nature of Nitric Acid
Nitric acid is a strong oxidizing agent. In reactions with metals, it tends to oxidize hydrogen rather than liberate it when reacting with most metals. However, magnesium and manganese are exceptions that can liberate hydrogen.

### Step 5: Conclusion
Among the given options, magnesium is the only metal that can liberate hydrogen when treated with nitric acid. Therefore, the answer is:
**Magnesium (Mg)**.

### Summary of Findings
- **Zinc**: Can liberate hydrogen but not with dilute HNO3.
- **Copper**: Cannot liberate hydrogen.
- **Magnesium**: Can liberate hydrogen.
- **Mercury**: Cannot liberate hydrogen.

### Final Answer
**Magnesium (Mg)** is the metal that liberates hydrogen when treated with nitric acid.

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