Which of the following properties is less for $D_2O$ than $H_2O$?

When zeolite,which is hydrated sodium aluminium silicate,is treated with hard water,the sodium ions are exchanged with

$D_2O$ is used in

Which can be used to prepare pure and demineralised $H_2O$ ?

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

In the following reactions,the total number of oxygen atoms in $X$ and $Y$ is $........$.
$Na_2O + H_2O \rightarrow 2 X$
$Cl_2O_7 + H_2O \rightarrow 2 Y$