Which of the following alkali metal carbonates is thermally unstable and decomposes upon heating?

Solution

1. Alkali metal carbonates are generally stable towards heat except for lithium carbonate.
2. The small size of the ${\text{Li}}^{+}$ ion leads to high polarising power.
3. ${\text{Li}}_2{\text{CO}}_3\stackrel{\Delta }{\to }{\text{Li}}_2\text{O}+{\text{CO}}_2$.
4. Hence the answer is (A).