Which of the following pairs of atomic numbers represents elements belonging to the $s$-block?

Match the following items in Column-$I$ with the corresponding items in Column-$II$.

Column-$I$	Column-$II$
$I$. $Na_2CO_3 \cdot 10H_2O$	$A$. Portland cement ingredient
$II$. $Mg(HCO_3)_2$	$B$. Castner-Kellner process
$III$. $NaOH$	$C$. Solvay process
$IV$. $Ca_3Al_2O_6$	$D$. Temporary hardness

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: $KF > KCl > KBr > KI$

Match Column-$I$ with Column-$II$ :

Column-$I$	Column-$II$
$(a)$ $NaOH$	$(p)$ Silvine
$(b)$ $Na_2CO_3$	$(q)$ As cooling agent in nuclear reactor
$(c)$ Liquid $Na$	$(r)$ Detergent soap
$(d)$ Potassium	$(s)$ In purification of Bauxite

What products are formed when $1 \ mol$ of calcium phosphide reacts with an excess of water?

$A$ white solid '$A$' on heating produces a gas that turns lime water milky,and the remaining solid residue is yellow when hot but turns white on cooling. The solid '$A$' is: