The solubility of carbonates of alkaline earth metals decreases down the group due to:

The carbonates of alkaline earth metals decompose on heating to give:
$I$. $CO_2$
$II$. Metal oxide
$III$. $H_2 O$
$IV$. $CO$

Which of the following ions forms a hydroxide that is readily soluble in water?

Identify the correct statements with respect to compounds of Beryllium:
$I$. Beryllium oxide is amphoteric in nature.
$II$. Beryllium hydride is formed by the reaction of beryllium with hydrogen.
$III$. Beryllium hydride is formed by the reaction of beryllium chloride with lithium aluminium hydride.
$IV$. Beryllium sulphate is the least soluble sulphate among the sulphates of alkaline earth metals.

The covalent alkaline earth metal halide $(X = Cl, Br, I)$ is:

$X + C + Cl_2 \xrightarrow{1000 \ K} Y + CO;$
$Y + 2H_2O \rightarrow Z + 2HCl$
Compound $Y$ is found in a polymeric chain structure and is an electron-deficient molecule. $Y$ must be: