Furthermore (and it's hard to know this when you're starting out with chemistry, so I'm just going to tell you,) a dilute solution of NaOH is not going to digest citric acid down to CO2. Then only thing that happens is the reaction with citric acid's 3 free acid protons, not every single hydrogen in the molecule. You'll learn that towards the end of your second year of university organic chemistry, or you teacher should have given you this hint sooner.