In the presence of acid, phenol red turns yellow. As the pH rises (becomes alkaline), the solution returns to red. Based on this explanation, the uptake of CO2 by a plant in distilled water containing CO2 and a drop of phenol red would cause the water solution to.

Turn Yellow

Explanation:

Phenol red turns yellow in an acidic medium and red in a basic(alkaline medium) based on the explanation above.

A solution of carbon dioxide is slightly acidic however in the real sense carbon dioxide is not an acid. The acidic property is caused by the formation of carbonic acid (H2CO3) when CO2 is dissolved in water.

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