The one that is $NOT$ suitable for the removal of permanent hardness of water is :

What is Calgon,used for softening water?

The solubility of an ionic compound is compared in heavy water $(D_2O)$ and simple water $(H_2O)$. It is:

Given below are two statements: One is labelled as Assertion $A$ and the other labelled as Reason $R$.
Assertion $A$: During the boiling of water having temporary hardness,$Mg(HCO_3)_2$ is converted to $MgCO_3$.
Reason $R$: The solubility product of $Mg(OH)_2$ is greater than that of $MgCO_3$.
In the light of the above statements,choose the most appropriate answer from the options given below.

The velocity of neutrons in a nuclear reactor is slowed down by

$D_2O$ is preferred to $H_2O$ as a moderator in nuclear reactors because: