Assertion :  As the electropositive character increases down the group, the stability of carbonates and hydrogen carbonates of alkali metals increases.

Reason :  Lithium carbonates is not so stable to heat : lithium being very small in size polarises a large $C{O}_{3}^{-2}$ ion leading to the formation of more stable $L{i}_{2}O$ and $C{O}_{2}$

1. If both the assertion and the reason are true and the reason is a correct explanation of the assertion
2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
3. If the assertion is true but the reason is false
4. If both the assertion and reason are false