Which of the following can be added to remove the permanent hardness of water?

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 one of the following is not a method to remove permanent hardness of water?

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

Heavy water is a compound of

Provide general information about water $(H_2O)$.