Select the correct statement(s) about Group 2 carbonates.

AThe decomposition temperature of $MgCO X_{3}$ is higher than that of $SrCO X_{3}$ .
BThe decomposition $CaCO X_{3} CaO + CO X_{2}$ is exothermic.
C $BaCO X_{3}$ decomposes at a higher temperature than $CaCO X_{3}$ .
D $BeCO X_{3}$ is so unstable that it is kept in an atmosphere of $CO X_{2}$ .

Answer: C, D

Polarising power falls down the group, so decomposition temperature rises:

BeCO X_{3} < MgCO X_{3} < CaCO X_{3} < SrCO X_{3} < BaCO X_{3}

. This means

BaCO X_{3}

is more stable than

CaCO X_{3}

and

MgCO X_{3}

is less stable than

SrCO X_{3}

. Breaking the carbonate needs heat, so calcination is endothermic. Only the first two statements are correct.