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

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$A$. Chlorophyll	$I$. $Na_2CO_3$
$B$. Soda ash	$II$. $CaSO_4$
$C$. Dentistry,Ornamental work	$III$. $Mg^{2+}$
$D$. Used in white washing	$IV$. $Ca(OH)_2$

Choose the correct answer from the options given below:

What is the nature of metal nitrates?

Which of the following order$(s)$ is/are correct?
$(A)$ Thermal stability: $BeSO_4 < MgSO_4 < CaSO_4 < SrSO_4$
$(B)$ Melting point: $NaCl > KCl > RbCl > CsCl$
$(C)$ Solubility: $LiOH < NaOH$
$(D)$ Lattice energy: $KF > KCl > KBr > KI$

Select the incorrect order.

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 |