Which of the following mixtures is known as fusion mixture?

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 $LiH < NaH < KH < RbH < CsH$.

Match the constituents of cements with their percentage proportion :

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

Which of the following is not true about potash alum?

Match the following columns:

Column-$I$	Column-$II$
$(i)$ Solvay process	$(p)$ $Na_2O$
$(ii)$ Evolve $CO_2$ on heating	$(q)$ $Na_2O_2$
$(iii)$ Aqueous solution is not neutral towards litmus	$(r)$ $NaHCO_3$
$(iv)$ Used as air purifier in submarine	$(s)$ $Na_2CO_3$

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: $KF > KCl > KBr > KI$