Which of the following substances is the least soluble in water?

The following compounds have been arranged in order of their increasing thermal stabilities. Identify the correct order.
$K_2CO_3$ $(I)$
$MgCO_3$ $(II)$
$CaCO_3$ $(III)$
$BeCO_3$ $(IV)$

$CaCO_3$ $\xrightarrow[excess \ H_2O]{CO_2 \ in} A$ $\xrightarrow{\Delta} B$
Identify $A$ and $B$.

The alkaline earth metal that imparts apple green colour to the Bunsen flame when introduced in it in the form of its chloride is

Consider the following reaction sequence:
$CaO + CO_2 \to A$
$A \xrightarrow{\Delta} B + CO_2$
$B + H_2O \to C$
$C + CO_2 \to D$
$D + H_2O + CO_2 \to E$
Identify compounds $D$ and $E$.

What is slaking of lime?