The metal salts formed during the softening of hard water using $Clark's$ method are:

Which of the following statements is/are correct?

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T$.: $Na\underline{H} + H_2O \longrightarrow NaOH + H_2 \uparrow$

Match List-$I$ with List-$II$ and select the correct answer using the codes given below.

List-$I$	List-$II$
$1.$ Heavy water	$(a)$ Bicarbonates of $Ca$ and $Mg$ 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 $Ca$ and $Mg$ in water

Which of the following methods is used for the removal of only temporary hardness of water?

Assertion $(A)$ : $NaCl$ is less soluble in heavy water than in ordinary water.
Reason $(R)$ : Dielectric constant of ordinary water is more than that of heavy water.
The correct answer is