Concept:Soda water gets its fizz from carbon dioxide gas dissolved under pressure, forming carbonic acid.Explanation:When carbon dioxide (CO2​) is forced into water at high pressure, it dissolves and creates the bubbles and slightly acidic taste characteristic of soda water. This process is called carbonation. Carbon monoxide is toxic and not used; oxygen and marsh gas (methane) do not produce the desired fizzy drink.Answer:Option B: Carbon dioxide.