When a mixture of anhydrous `Na_2CO_3 and NaHCO_3` is heated to `100^@C`, a loss in mass is recorded. This is due to

Options

A. decomposition of `Na_2CO_3` alone
B. decomposition of `NaHCO_3` alone
C. decomposition of both
D. removal of water of crystallisation

Explanation

To solve the question regarding the loss in mass when a mixture of anhydrous sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃) is heated to 100°C, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components**:
- The mixture consists of anhydrous sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃).

2. **Understand the Stability of Components**:
- Anhydrous sodium carbonate (Na₂CO₃) is stable when heated and does not decompose.
- Sodium bicarbonate (NaHCO₃), on the other hand, is not stable at elevated temperatures and decomposes upon heating.

3. **Write the Decomposition Reaction**:
- When sodium bicarbonate is heated, it decomposes according to the following reaction:
\[ 2 \, \text{NaHCO}_3 (s) \rightarrow \text{Na}_2\text{CO}_3 (s) + \text{H}_2\text{O} (g) + \text{CO}_2 (g) \]
- This reaction indicates that sodium bicarbonate breaks down into sodium carbonate, water vapor, and carbon dioxide gas.

4. **Analyze the Loss in Mass**:
- The loss in mass recorded during the heating process is primarily due to the release of water vapor (H₂O) and carbon dioxide gas (CO₂) from the decomposition of sodium bicarbonate.
- Since anhydrous sodium carbonate does not change, it does not contribute to any loss in mass.

5. **Conclusion**:
- Therefore, the loss in mass when the mixture is heated to 100°C is due to the decomposition of sodium bicarbonate (NaHCO₃), which releases gaseous products.

### Final Answer:
The loss in mass is due to the decomposition of sodium bicarbonate (NaHCO₃) into sodium carbonate (Na₂CO₃), water (H₂O), and carbon dioxide (CO₂) upon heating.

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