Permanent hardness cannot be removed by

Which of the following is a good scientific method to detect the presence of water in a liquid?

Write chemical reactions to show the amphoteric nature of water.

When the first element of the periodic table is treated with dioxygen,it gives a compound whose solid state floats on its liquid state. This compound has an ability to act as an acid as well as a base. What products will be formed when this compound undergoes autoionisation?

Assertion $(A)$ : $NaCl$ is less soluble in heavy water than in ordinary water.
Reason $(R)$ : Dielectric constant of ordinary water is more than that of heavy water.
The correct answer is

Which of the following is not true about the $H_2O$ molecule?