Which one of the following methods is most suitable for preparing deionized water?

When zeolite is treated with hard water,the sodium ions are exchanged with:

Temporary hardness of water can be removed by

$A$ 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 freezing point of heavy water at $1 \ atm$ pressure is: (in $^{\circ}C$)

Water obtained by purification with organic ion exchange resins is: