Highest melting point among the following is displayed by

Group $2$ hydrides with significant covalent character is/are:

$CO_2$ is passed through lime water. Initially,the solution turns milky and then becomes clear upon continued bubbling of $CO_2$. The clear solution is due to the formation of:

Chemical $A$ is used for water softening to remove temporary hardness. $A$ reacts with $Na_2CO_3$ to generate caustic soda. When $CO_2$ is bubbled through $A$,it turns cloudy. What is the chemical formula of $A$?

Which of the following ions has a higher hydration enthalpy than the $Mg^{2+}$ ion?

Why do beryllium and magnesium not impart colour to the flame in the flame test?