What is used to soften water by the Clark's method?

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

The hydride ion $H^{-}$ is a stronger base than the hydroxide ion $OH^{-}$. Which of the following reactions will occur if sodium hydride $(NaH)$ is dissolved in water?

When zeolite is treated with hard water,the sodium ions are exchanged with:

Match List $I$ with List $II$ and select the correct answer using the codes given below the lists:

$1.$ Heavy water	$a.$ Bicarbonates of $Mg$ and $Ca$ in water
$2.$ Temporary hard water	$b.$ No foreign ions in water
$3.$ Soft water	$c.$ $D_2O$
$4.$ Permanent hard water	$d.$ Sulphates and chlorides of $Mg$ and $Ca$ in water

Some statements about heavy water are given below:
$(i)$ Heavy water is used as a moderator in nuclear reactors.
$(ii)$ Heavy water is more associated than ordinary water.
$(iii)$ Heavy water is more effective solvent than ordinary water.
Which of the above statements are correct?