In Clark's method,the chemical used is:

Which of the following ions are responsible for the hardness of water?

Explain: Proton $(H^{+})$ does not exist in aqueous solution.

Statements about heavy water are given below.
$A.$ Heavy water is used in exchange reactions for the study of reaction mechanisms.
$B.$ Heavy water is prepared by exhaustive electrolysis of water.
$C.$ Heavy water has higher boiling point than ordinary water.
$D.$ Viscosity of $H_2O$ is greater than $D_2O$.

What is $Calgon$,used as a water softener?

The compound used as a moderator in nuclear reactors is