Which of the following substance on being heated will give a gas that does not turns lime water milky :-

Options

A. `Na_2CO_(3)`
B. `ZnCO_(3)`
C. `ZnSO_(3)`
D. `MgCO_(3)`

Explanation

To determine which substance, when heated, produces a gas that does not turn lime water milky, we need to analyze the thermal decomposition of each given compound. The compounds provided are Na2CO3 (sodium carbonate), ZnCO3 (zinc carbonate), ZnSO3 (zinc sulfide), and MgCO3 (magnesium carbonate).

### Step-by-Step Solution:

1. **Understanding Lime Water**:
- Lime water is a solution of calcium hydroxide (Ca(OH)2).
- It turns milky when carbon dioxide (CO2) is bubbled through it, forming calcium carbonate (CaCO3), which is a white precipitate.

2. **Analyzing Each Compound**:
- **Na2CO3 (Sodium Carbonate)**:
- Upon heating, it decomposes to form sodium oxide (Na2O) and carbon dioxide (CO2).
- CO2 will turn lime water milky.

- **ZnCO3 (Zinc Carbonate)**:
- Upon heating, it decomposes to form zinc oxide (ZnO) and carbon dioxide (CO2).
- CO2 will turn lime water milky.

- **ZnSO3 (Zinc Sulfide)**:
- Upon heating, it decomposes to form zinc oxide (ZnO) and sulfur dioxide (SO2).
- SO2 does not react with lime water, hence it will not turn it milky.

- **MgCO3 (Magnesium Carbonate)**:
- Upon heating, it decomposes to form magnesium oxide (MgO) and carbon dioxide (CO2).
- CO2 will turn lime water milky.

3. **Conclusion**:
- Among the four substances, Na2CO3, ZnCO3, and MgCO3 all produce CO2, which turns lime water milky.
- ZnSO3 produces SO2, which does not turn lime water milky.
- Therefore, the correct answer is **ZnSO3**.

### Final Answer:
The substance that, when heated, will give a gas that does not turn lime water milky is **ZnSO3**.

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