$CuSO_4$ solution $+$ lime is called

Match the correct option from Column $-A$ and Column $-B$.

Column $-A$	Column $-B$
$(1).$ Calgon	$(a).$ $D_2O$
$(2).$ Perhydrol	$(b).$ Zeolite
$(3).$ Heavy water	$(c).$ Sodium hexametaphosphate
$(4).$ Aluminosilicate	$(d).$ Commercial name of Hydrogen peroxide

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.

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

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

When oxalic acid reacts with conc. $H_2SO_4$,two gases produced are of neutral and acidic in nature respectively. Potassium hydroxide absorbs one of the two gases. The product formed during this absorption and the gas which gets absorbed are respectively