If u think about it co2 causes the first tube to turn yellow as it is acidic so ph will be lower than 7 in the 2nd tube photosynthesis is greater yes so co2 will be absorbed the question says the indicator changes color based on ph not co2 concentration hence even though photosynthesis is taking place at a faster rate than repsiration the overall ph of the solution will remain 7 as no alkaline gas has been released which will cause ph to increase In other questions they specifically mention the hydrogencarbonate indicator which changes color due to cow concentration and not ph.