Which can be used to prepare pure and demineralised $H_2O$ ?

Amongst the following,the form of water with the lowest ionic conductance at $298 \ K$ is

In solid ice, an oxygen atom is surrounded by:

The $INCORRECT$ statement$(s)$ about heavy water is (are):
$(A)$ Used as a moderator in nuclear reactor.
$(B)$ Obtained as a by-product in fertilizer industry.
$(C)$ Used for the study of reaction mechanism.
$(D)$ Has a higher dielectric constant than water.
Choose the correct answer from the options given below:

Which of the following is not true?

Polyphosphates are used as water softening agents because: