Which of the following statements does not define the characteristic property of water,"Water is a universal solvent"?

Hardness of water is due to the presence of salts of

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?

Permanent hardness in water is due to the presence of which of the following ions?

The freezing point of heavy water at $1 \ atm$ pressure is: (in $^{\circ}C$)

Choose the correct statement about various water softening methods.