Why does soda contain co2?

Answer 1

Carbon Dioxide is present in the soda (drinks) to give the fluid a pleasant fizz and agreeable taste. . Most people find this refreshing and soda which has been allowed to go flat is not seen as palatable. Carbon dioxide was chosen rather than air or nitrogen as the "fizz" as more of it dissolves in the fluid by actually combining with the water to form carbonic acid and is released more slowly than air or other gases.

As an added benefit the slightly acidic taste of carbon dioxide in water make the drink seem better. The difference is obvious when carbonated water and still water is compared.

Answer 2

CO2 is dissolved in soda water to make it fizz.