How is heavy water prepared? Compare its physical properties with those of ordinary water.

(N/A) Heavy water $(D_{2}O)$ is prepared by the prolonged electrolysis of ordinary water $(H_{2}O)$. Since $H_{2}O$ is electrolyzed faster than $D_{2}O$,the remaining water becomes enriched in $D_{2}O$.
The physical properties of $H_{2}O$ and $D_{2}O$ are compared in the table below:

Property	$H_{2}O$	$D_{2}O$
Molecular mass $(g \ mol^{-1})$	$18.0151$	$20.0276$
Melting point $(K)$	$273.0$	$276.8$
Boiling point $(K)$	$373.0$	$374.4$
Enthalpy of formation $(kJ \ mol^{-1})$	$-285.9$	$-294.6$
Enthalpy of vaporisation at $373 \ K$ $(kJ \ mol^{-1})$	$40.66$	$41.61$
Enthalpy of fusion $(kJ \ mol^{-1})$	$6.01$	$6.28$
Temperature of max. density $(K)$	$276.98$	$284.2$
Density at $298 \ K$ $(g \ cm^{-3})$	$1.0000$	$1.1059$
Viscosity (centipoise)	$0.8903$	$1.107$
Dielectric constant $(C^{2} / Nm^{2})$	$78.39$	$78.06$
Electrical conductivity at $298 \ K$ $(ohm^{-1} \ cm^{-1})$	$5.7 \times 10^{-8}$	$3.0 \times 10^{-8}$