State the reasons why

(i) boiled water tastes flat

(ii) a soda water bottle opens with a 'fizz'.

(i) As soluble gases in water contribute to the taste of water and on boiling, the temperature of the water increases, thereby the solubility of the dissolved gases decreases and the dissolved gases are expelled out. Hence, the water tastes flat.

(ii) Soda contains carbon dioxide dissolved in water under pressure.
Solubility of carbon dioxide under normal atmospheric pressure is very low, but when subjected to high pressure, it dissolves to a great extent as in case of soda water in which carbon dioxide is dissolved in water under pressure and the bottle is corked.
On opening the bottle, the gas rapidly bubbles out with a 'fizz', since the pressure on the surface of the water suddenly decreases and so does the solubility of carbon dioxide gas in water.