Which of the following is the best scientific method to test the presence of water in a liquid?

Permanent hardness in water cannot be cured by

$100 \, mL$ 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 $146 \, g \, mol^{-1}$)

We use polymetaphosphates as water softeners as they:

Choose the correct statement about various water softening methods.

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