which of the soft drinks has the highest amount of CO2 (= carbon dioxide) dissolved in it?

Answer 1

They al have the same amount, what makes them more or less fizzy depends on how much extra crap is in it. Syrup weights them down, making them less fizzy.

This is why a bottle of Coca Cola goes flat in less than a half hour, but club soda can stay fizzy for hours on end.

Answer 2

Just from personal soda drinking experience, I would say Sprite. It is super fizzy at the start - make my nose tingle for like half a can, then starts to be fizzy like normal soda.

Answer 3

I would say Diet Coke, from it's ability to fizz violently with a Mentos.