Assertion : When 10 g of `CaCO_3` is decomposed, 5.6 g of residue is left and 4.4 g of `CO_(2)` escapes.
Reason : Law of conservation of mass is followed.

Answer

To solve the problem, we need to analyze the assertion and the reason given.

### Step-by-Step Solution:

1. **Identify the Reaction**:
When calcium carbonate (CaCO₃) decomposes, it produces calcium oxide (CaO) and carbon dioxide (CO₂). The balanced equation for this reaction is:
\[ \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \]

2. **Given Data**:
- Mass of CaCO₃ before decomposition = 10 g
- Mass of residue (CaO) after decomposition = 5.6 g
- Mass of CO₂ released = 4.4 g

3. **Check the Law of Conservation of Mass**:
According to the law of conservation of mass, the total mass of the reactants must equal the total mass of the products.

- Total mass of products = Mass of CaO + Mass of CO₂
\[ \text{Total mass of products} = 5.6 \, \text{g} + 4.4 \, \text{g} = 10 \, \text{g} \]

4. **Conclusion**:
Since the total mass of the products (10 g) is equal to the mass of the reactants (10 g), the law of conservation of mass is upheld in this reaction.

5. **Assertion and Reason Evaluation**:
- **Assertion**: When 10 g of CaCO₃ is decomposed, 5.6 g of residue is left and 4.4 g of CO₂ escapes. (This is true based on the given data.)
- **Reason**: Law of conservation of mass is followed. (This is also true as shown in the calculations.)

Therefore, both the assertion and the reason are correct, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion and the reason are correct, and the reason is the correct explanation of the assertion.

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