Oxygen was discovered by

Which of the following statements is not true?

$100 \, mL$ of a water sample contains $0.81 \, g$ of calcium bicarbonate and $0.73 \, g$ of magnesium bicarbonate. The hardness of this water sample expressed in terms of equivalents of $CaCO_3$ is .............. $ppm$ (molar mass of calcium bicarbonate is $162 \, g \, mol^{-1}$ and magnesium bicarbonate is $146 \, g \, mol^{-1}$)

Match List $I$ with List $II$ and select the correct answer using the codes given below the lists:

$1.$ Heavy water	$a.$ Bicarbonates of $Mg$ and $Ca$ in water
$2.$ Temporary hard water	$b.$ No foreign ions in water
$3.$ Soft water	$c.$ $D_2O$
$4.$ Permanent hard water	$d.$ Sulphates and chlorides of $Mg$ and $Ca$ in water

Heavy water $(D_2O)$ is

Is demineralised or distilled water useful for drinking purposes? If not,how can it be made useful?