Final answer:
When exposed to ammonia, which is a base, phenolphthalein changes to a pink or red color (option C) due to the increase in pH above 8.3 where it reacts to the lack of hydrogen ions.
Step-by-step explanation:
Phenolphthalein changes color in the presence of different pH levels due to its properties as an acid-base indicator. In the presence of a base, such as ammonia, phenolphthalein undergoes a change in its molecular structure which alters its color.
When exposed to basic substances, with a pH greater than 8.3, phenolphthalein will turn from colorless to a pink or red color (option C) . Therefore, in the presence of ammonia, a basic substance, phenolphthalein would change to a pink color.