Upon brining the flame of a burning matchstick or candle near which of these reactions will you not be able to hear a pop sound?

Options

A. Reaction between sodium and cold water
B. Reaction between magnesium and oxygen
C. Reaction between zinc and dilute sulphuric acid
D. Reaction between aluminium and dilute hydrochloric acid

Answer

To determine which reaction will not produce a pop sound when the flame of a burning matchstick or candle is brought near it, we need to analyze the reactions given in the options and see if they produce hydrogen gas (H2). The pop sound is a characteristic test for hydrogen gas.

### Step-by-Step Solution:

1. **Understand the Pop Sound Test**:
- The pop sound is produced when hydrogen gas (H2) burns in the presence of a flame. Therefore, we need to identify which reactions produce hydrogen gas.

2. **Analyze Each Option**:
- **Option 1: Reaction between Sodium and Cold Water**:
- Reaction: \( \text{Na} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2 \)
- This reaction produces hydrogen gas (H2). Therefore, a pop sound will be heard.

- **Option 2: Reaction between Magnesium and Oxygen**:
- Reaction: \( \text{Mg} + \text{O}_2 \rightarrow \text{MgO} \)
- This reaction does not produce hydrogen gas. Therefore, no pop sound will be heard.

- **Option 3: Reaction between Zinc and Dilute Sulfuric Acid**:
- Reaction: \( \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \)
- This reaction produces hydrogen gas (H2). Therefore, a pop sound will be heard.

- **Option 4: Reaction between Aluminum and Dilute Hydrochloric Acid**:
- Reaction: \( \text{Al} + \text{HCl} \rightarrow \text{AlCl}_3 + \text{H}_2 \)
- This reaction also produces hydrogen gas (H2). Therefore, a pop sound will be heard.

3. **Conclusion**:
- The only reaction that does not produce hydrogen gas and therefore will not produce a pop sound is the reaction between magnesium and oxygen.

### Final Answer:
The reaction between magnesium and oxygen (Option 2) will not produce a pop sound when the flame of a burning matchstick or candle is brought near it.

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