Which of the following pairs will not produce dihydrogen gas ?

Options

A. `Cu+HCl`
B. `Fe+H_(2)SO_(4)`
C. `Mg+"Steam"`
D. `Na+"alcohol"`

Answer

To determine which of the following pairs will not produce dihydrogen gas (H₂), we will analyze each pair of reactants given in the options.

### Step-by-Step Solution:

1. **Analyze the first pair: Cu + HCl**
- Copper (Cu) is less reactive than hydrogen. Therefore, it cannot displace hydrogen from hydrochloric acid (HCl).
- **Conclusion**: No reaction occurs, and thus, no dihydrogen gas is produced.

2. **Analyze the second pair: Fe + H₂SO₄**
- Iron (Fe) is more reactive than hydrogen. It can displace hydrogen from sulfuric acid (H₂SO₄).
- The reaction is:
\[ \text{Fe} + \text{H}_2\text{SO}_4 \rightarrow \text{FeSO}_4 + \text{H}_2 \]
- **Conclusion**: Dihydrogen gas is produced.

3. **Analyze the third pair: Mg + Steam**
- Magnesium (Mg) reacts with steam (H₂O in gaseous form) to produce magnesium oxide (MgO) and dihydrogen gas.
- The reaction is:
\[ \text{Mg} + \text{H}_2\text{O} \rightarrow \text{MgO} + \text{H}_2 \]
- **Conclusion**: Dihydrogen gas is produced.

4. **Analyze the fourth pair: Na + Alcohol**
- Sodium (Na) reacts with alcohol (like ethanol, C₂H₅OH) to produce sodium ethoxide (C₂H₅ONa) and dihydrogen gas.
- The reaction is:
\[ \text{Na} + \text{C}_2\text{H}_5\text{OH} \rightarrow \text{C}_2\text{H}_5\text{ONa} + \text{H}_2 \]
- **Conclusion**: Dihydrogen gas is produced.

### Final Conclusion:
From the analysis, the only pair that does not produce dihydrogen gas is **Cu + HCl**.

### Answer:
The correct option is **Cu + HCl**.

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