Li2CO3 decomposes to Li2O and CO2 on moderate heating, whereas Na2CO3 and K2CO3 are stable. The best explanation is that

the small Li+ polarises CO3^2- strongly and the product Li2O is stabilised by a high lattice energy with the small cation

Li+ is larger than Na+ and hence polarises weakly

Li2CO3 is more ionic than Na2CO3

Li has a lower ionisation energy than Na

JEE Advanced levelSingle correct optionDifficulty 3 of 3cb201

$Li X_{2} CO X_{3}$ decomposes to $Li X_{2} O$ and $CO X_{2}$ on moderate heating, whereas $Na X_{2} CO X_{3}$ and $K X_{2} CO X_{3}$ are stable. The best explanation is that

Athe small $Li X^{+}$ polarises $CO X_{3} X^{2 -}$ strongly and the product $Li X_{2} O$ is stabilised by a high lattice energy with the small cation
B $Li X^{+}$ is larger than $Na X^{+}$ and hence polarises weakly
C $Li X_{2} CO X_{3}$ is more ionic than $Na X_{2} CO X_{3}$
D $Li$ has a lower ionisation energy than $Na$

Decomposition requires polarisation of the carbonate ion so that one C-O bond weakens and

CO X_{2}

is expelled, leaving the oxide ion. The small

Li X^{+}

is the best at this and also forms an oxide with a large lattice energy with the small

O X^{2 -}

. Larger

Na X^{+}

and

K X^{+}

do neither as strongly, so their carbonates are stable.