In polymeric $(BeCl_2)_n$,there are

Among the sulphates of alkaline earth metals,the solubilities of $BeSO_4$ and $MgSO_4$ in water,respectively,are

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

Given below are two statements:
Statement $I$: None of the alkaline earth metal hydroxides dissolve in alkali.
Statement $II$: Solubility of alkaline earth metal hydroxides in water increases down the group.
In the light of the above statements,choose the most appropriate answer from the options given below:

The compound $A$ on heating gives a colourless gas and a residue that is dissolved in water to obtain $B$. Excess of $CO_2$ is bubbled through aqueous solution of $B$,$C$ is formed which is recovered in the solid form. Solid $C$ on gentle heating gives back $A$. The compound $A$ is:

$Be(OH)_2$ is insoluble in water while $Ba(OH)_2$ is highly soluble due to: