The method used to remove temporary hardness of water is

The substance used as a universal solvent is .....

$A$ sample of water contains $30 \ ppm$ of $MgSO_4$ and $19 \ ppm$ of $MgCl_2$. Calculate the hardness of water in $ppm$ (in terms of $CaCO_3$ equivalents).

The degree of hardness of water is generally expressed in terms of which of the following?

Which of the following methods is used for the removal of only temporary hardness of water?

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 $D_2O$.