White vitriol is .......

Match the following substances in List-$I$ with their uses in List-$II$:
| List-$I$ (Substance) | List-$II$ (Use) |
| :--- | :--- |
| $(A)$ $Na_2O_2$ | $(I)$ Photoelectric cells |
| $(B)$ $D_2O$ | $(II)$ Antacid |
| $(C)$ $Cs$ | $(III)$ Oxidising agent |
| $(D)$ $Mg(OH)_2$ | $(IV)$ Moderator |

Give a brief account of the abundance of alkali metals and alkaline earth metals in the Earth's crust.

$A$ red coloured mixed oxide $(X)$ on treatment with conc. $HNO_3$ gives a compound $(Y).$ $(Y)$ with $HCl$ produces a chloride compound $(Z)$ which can also be produced by treating $(X)$ with conc. $HCl.$ Compounds $(X),$ $(Y),$ and $(Z)$ will be

What is the mixture of $MgCl_2$ and $MgO$ called?

Match the constituents of cements with their percentage proportion :

Constituents	Percentage
$1$. $CaO$	$a$. $2-3\%$
$2$. $MgO$	$b$. $50-60\%$
$3$. $SiO_2$	$c$. $5-10\%$
$4$. $Al_2O_3$	$d$. $20-25\%$