$A$ hydrated solid $X$ on heating initially gives a monohydrated compound $Y$. $Y$ upon heating above $373 \ K$ leads to an anhydrous white powder $Z$. $X$ and $Z$,respectively,are

Match column-$I$ with column-$II$ :

column-$I$	column-$II$
$a$. $Ra$	$p$. Aeroplane industry
$b$. $K$	$q$. Down cell
$c$. $Li$	$r$. Photo electric cell
$d$. $Na$	$s$. Radioactive

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 |

Choose the correct statement and mark the correct option given below:
$(a)$ $AgF$ is soluble and colourless in aqueous medium.
$(b)$ For $LiF$,solubility and melting point are both lower as compared to $NaF$.
$(c)$ Solubility of $Rb_2SO_4$ is less as compared to $BaSO_4$.
$(d)$ If $AgI$ is added to water,the colour of water will turn yellow from colourless.

The correct statements among the following are:
$(A)$ $BeH_2$ and $MgH_2$ are polymeric in nature.
$(B)$ $LiH$ is unreactive to oxygen at moderate temperatures.
$(C)$ $BeH_2$ and $MgH_2$ possess significant covalent character.
$(D)$ The stability of alkali metal hydrides follows the order $LiH < NaH < KH < RbH < CsH$.

$A$ pink colored salt on dry heating becomes blue in colour. The salt may contain: