Identify the correct statements from the following:
$I$. All alkaline earth metals give hydrides on heating with hydrogen.
$II$. Calcium hydroxide is used to purify sugar.
$III$. $BeCl_2$ is a dimer in gaseous phase.

Highest melting point among the following is displayed by

When water is added to compound $(A)$ of calcium,a solution of compound $(B)$ is formed. When carbon dioxide is passed into the solution,it turns milky due to the formation of compound $(C)$. If excess of carbon dioxide is passed into the solution,the milkiness disappears due to the formation of compound $(D)$. Identify the compounds $A$,$B$,$C$,and $D$. Explain why the milkiness disappears in the last step.

$A$ mixture of $MgCl_2$ and $MgO$ is called

An alkaline earth metal $(M)$ gives a salt with chlorine,which is insoluble in water at room temperature but soluble in boiling water. It also forms an insoluble sulphate whose mixture with a sulphide of a transition metal is called 'lithopone' - a white pigment. Metal $M$ is

How does Plaster of Paris become hard?