Which alkali metal carbonate is thermally unstable and why?

Explanation

**Step-by-Step Solution:**

1. **Identify the Alkali Metals**: The alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).

2. **Write the Formulas for Alkali Metal Carbonates**: The carbonates of these alkali metals are:
- Lithium carbonate: Li₂CO₃
- Sodium carbonate: Na₂CO₃
- Potassium carbonate: K₂CO₃
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