Compound having lowest thermal stability is:

Options

A. `NaHCO_(3)`
B. `KHCO_(3)`
C. `RbHCO_(3)`
D. `CsHCO_(3)`

Explanation

To determine which compound has the lowest thermal stability among the given options, we will analyze the thermal stability of alkali metal bicarbonates.

### Step-by-Step Solution:

1. **Understanding Thermal Stability**:
- Thermal stability refers to the ability of a compound to resist decomposition when subjected to heat. Compounds with lower thermal stability decompose at lower temperatures.

2. **Identify the Compounds**:
- The compounds given in the question are:
1. Sodium bicarbonate (NaHCO₃)
2. Potassium bicarbonate (KHCO₃)
3. Rubidium bicarbonate (RbHCO₃)
4. Cesium bicarbonate (CsHCO₃)

3. **Trend in Thermal Stability**:
- For alkali metal bicarbonates, thermal stability increases as we move down the group in the periodic table. This is because larger alkali metals form more stable compounds that require more heat to decompose.

4. **Decomposition Temperatures**:
- The decomposition temperatures for these bicarbonates are approximately:
- Sodium bicarbonate: decomposes around 80°C
- Potassium bicarbonate: decomposes around 100°C
- Rubidium bicarbonate: decomposes around 170°C
- Cesium bicarbonate: decomposes around 180°C

5. **Comparison of Thermal Stability**:
- From the decomposition temperatures, we can see that sodium bicarbonate decomposes at the lowest temperature (80°C), indicating that it has the lowest thermal stability among the options provided.

6. **Conclusion**:
- Therefore, the compound with the lowest thermal stability is **sodium bicarbonate (NaHCO₃)**.

### Final Answer:
The compound having the lowest thermal stability is **sodium bicarbonate (NaHCO₃)**.

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