Which of the following is a bad conductor of electricity?

Melting point,enthalpy of vaporisation and viscosity data of $H_2O$ and $D_2O$ is given below.

$Property$	$H_2O$ vs $D_2O$
$Melting$ $point/K$	$273.0$ vs $276.8$
$Enthalpy$ $of$ $vaporisation$ $at$ $(373 \ K) / kJ \ mol^{-1}$	$40.66$ vs $41.61$
$Viscosity/centipoise$	$0.8903$ vs $1.107$

On the basis of this data,explain in which of these liquids intermolecular forces are stronger?

The temperatures of maximum density in $H_2O$ and $D_2O$ respectively are:

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 process is used for the removal of hardness of water?

Describe the usefulness of water in the biosphere and biological systems.