Dihydrogen gas may be prepared by heating caustic soda on

Options

A. `Cu`
B. `Zn`
C. `Na`
D. `Ag`

Explanation

To solve the question "Dihydrogen gas may be prepared by heating caustic soda on," we need to identify the correct metal that can react with caustic soda (sodium hydroxide, NaOH) to produce dihydrogen gas (H₂).

### Step-by-Step Solution:

1. **Understanding Caustic Soda**:
- Caustic soda is the common name for sodium hydroxide (NaOH), which is a strong base.

2. **Identifying the Options**:
- The question provides four options, all of which are metals. We need to determine which metal can react with NaOH.

3. **Properties of Metals**:
- Most metals do not react with bases. However, some metals are amphoteric, meaning they can react with both acids and bases.

4. **Identifying Amphoteric Metals**:
- Among the common metals, zinc (Zn) is known to be amphoteric. This means it can react with strong bases like NaOH.

5. **Reaction of Zinc with Caustic Soda**:
- When zinc reacts with sodium hydroxide, it forms sodium zincate (Na₂ZnO₂) and releases dihydrogen gas (H₂).
- The balanced chemical equation for this reaction is:
\[ 2 \text{NaOH} + \text{Zn} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2 \]

6. **Conclusion**:
- Since zinc is the only metal among the options that can react with caustic soda to produce dihydrogen gas, the correct answer is **Zn**.

### Final Answer:
Dihydrogen gas may be prepared by heating caustic soda on **zinc (Zn)**.