a. Naturally hard water is usually preferred in drinking and soft water in working. Why?
b. How many types of heavy water are possible? Write down formulae of all possible heavy water molecules.

Explanation

a soft water is usually acidic and contains `Na^(o+)` ions in place of di- and trivalent metals ion. An increased intake of `Na^(o+)` is known to be related to heard diseas and moreover the acidic soft water is more likely to attack metallic pipes, resulting in the solution of dangerous ions such as `Pb^(2+)`. one way to avoid `Na^(o+)` ions in drinking water and to use less soap when washing would be to drink naturally hard water and work in soft water.
(b) These are six possible heavy water molecules, which are as follows: