Which of the following statements are correct?

A $Li X_{2} CO X_{3}$ is less thermally stable than $Na X_{2} CO X_{3}$ .
BThe thermal stability order is $BeCO X_{3} < MgCO X_{3} < CaCO X_{3}$ .
C $NaHCO X_{3}$ decomposes on heating to give $Na X_{2} CO X_{3}$ at a temperature at which $Na X_{2} CO X_{3}$ itself is stable.
D $K X_{2} CO X_{3}$ decomposes to the oxide more readily than $Li X_{2} CO X_{3}$ .

Answer: A, B, C

The smaller

Li X^{+}

polarises the carbonate ion more than

Na X^{+}

, so

Li X_{2} CO X_{3}

is less stable. Similarly the small

Be X^{2 +}

makes

BeCO X_{3}

the least stable group 2 carbonate.

2 NaHCO X_{3} Na X_{2} CO X_{3} + H X_{2} O + CO X_{2}

occurs near

400 K

while

Na X_{2} CO X_{3}

stays intact.

K X_{2} CO X_{3}

is much more stable than

Li X_{2} CO X_{3}

, so the last statement is wrong.