Why did the ph balance change during the light experiment?

When carbon dioxide is dissolved in water it results in the formation of Carbonic acid and the pH level gets drops.

Explanation:

pH is used to know the hydrogen ion concentration present in the solution.

photosynthesis light experiment fluctuates the pH balance due to their impacts on the carbon dioxide levels.

The light experiment initiates the photosynthesis,which result in the addition of carbon dioxide in water.

Carbon dioxide reacts with water to form carbonic acid, and the carbonic acid may lose its one or both hydrogen ions, the release of the hydrogen ions cause the pH level to drop.

Thus because of the carbonic acid formation the  pH balance change during the light experiment.

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.

i believe the answer would be b. hope it : )