$D_2O$ is used in

The reagent$(s)$ used for softening the temporary hardness of water is(are):
$(A)$ $Ca_3(PO_4)_2$
$(B)$ $Ca(OH)_2$
$(C)$ $Na_2CO_3$
$(D)$ $NaOCl$

Which of the following is not true about the $H_2O$ molecule?

Match the following:

List-$I$ (Reactions)	List-$II$ (Methods)
$A$. $Mg(HCO_3)_2 \rightarrow Mg(OH)_2 \downarrow + 2 CO_2 \uparrow$	$I$. Clark's method
$B$. $M^{2+} + Na_4P_6O_{18}^{2-} \rightarrow [Na_2MP_6O_{18}]^{2-} + 2 Na^{+}$	$II$. Ion exchange method
$C$. $Ca(HCO_3)_2 + Ca(OH)_2 \rightarrow 2 CaCO_3 + 2 H_2O$	$III$. Boiling
$D$. $2 NaZ + Ca^{2+}_{(aq)} \rightarrow 2 Na^{+} + CaZ_2$ ($Z$ = Zeolite)	$IV$. Calgon's method

Polyphosphates are used as water softening agents because:

The freezing point of heavy water at $1 \ atm$ pressure is: (in $^{\circ}C$)