Which of the following compounds is used for the softening of hard water by Clark's method?

Permutit is the technical name given to:

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

Reaction of calgon with hard water containing $Ca^{2+}$ ions produces:

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?

Give reasons.
$(i)$ Lakes freeze from top towards bottom.
$(ii)$ Ice floats on water.