The variables to be examined in relation to carbon dioxide use are the amount of light exposure and amount of dissolved CO2. Phenol red is yellow/orange under acidic conditions, that is when the pH of the solution is less than 7 (e.g. pH = 6). This occurs when the concentration of CO2 is high.
There are no states in the picture, but Na should have a "(s)" after it, and Cl2 should have a "(g)" after it. NaCl should have an "(s)". Chlorine is a diatomic element so it has a "2" subscript on it.
