Sodium oxalate on heating with conc. $H_2SO_4$ gives

Match the items in Column-$I$ with the relevant item in Column-$II$.

Column-$I$	Column-$II$
$A$. Hydrogen peroxide is used as a	$1$. zeolite
$B$. Used in Calgon method	$2$. perhydrol
$C$. Permanent hardness of hard water is removed by	$3$. sodium hexametaphosphate
	$4$. propellant

List-$I$ contains compounds and List-$II$ contains reactions.

List-$I$	List-$II$
$I$. $H_2O_2$	$P$. $Mg(HCO_3)_2 + Ca(OH)_2 \rightarrow$
$II$. $Mg(OH)_2$	$Q$. $BaO_2 + H_2SO_4 \rightarrow$
$III$. $BaCl_2$	$R$. $Ca(OH)_2 + MgCl_2 \rightarrow$
$IV$. $CaCO_3$	$S$. $BaO_2 + HCl \rightarrow$
	$T$. $Ca(HCO_3)_2 + Ca(OH)_2 \rightarrow$

Match each compound in List-$I$ with its formation reaction$(s)$ in List-$II$,and choose the correct option.

Fill in the blanks:
$(1)$ Only $..........$ element of group $-6$ forms hydride.
$(2)$ $..........$ is used as a moderator in nuclear reactors.
$(3)$ The three-dimensional arrangement in ice occurs due to $..........$ bonding.
$(4)$ $..........$ method is used to obtain $H_2O_2$ from $2-$ethylanthraquinol.

$CuSO_4$ solution $+$ lime is called

The order $H_2O < H_2O_2$ is correct for which of the following properties?