The colour of the phenol red-containing solution would shift toward yellow.
Carbon dioxide is a colourless and acidic gas that is found in trace amounts in the atmosphere. When it reacts with water, carbonic acid is formed.
One of the properties of an acid is that it has the ability to turn blue litmus paper to red.
When Carbondioxide is used as a reactant, the phenol red-containing solution will shift toward yellow because the pH of the solution is less than 7 and turns blue as carbon dioxide is consumed and the pH of the solution rises to 7 or greater.
Note that acidity is pH of 0- 6 and basic solutions are from 8 - 14 in a pH scale.
Therefore, the colour of the phenol red-containing solution would shift toward yellow.
Learn more about acids here:
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