Question

when does phenolphthalein turn pink?
○ in the presence of a base
○ in the presence of an acid
○ when it is in a neutral solution
○ when it is reacting with a metal

Explanation:

Phenolphthalein is an acid - base indicator. Its characteristic is that it is colorless in acidic and neutral solutions, and it turns pink (or magenta) in basic (alkaline) solutions. Reacting with a metal is not related to its color change mechanism for indicating acidity or basicity, and it does not turn pink in acid or neutral solutions. So the correct option is "in the presence of a base".

Answer:

A. in the presence of a base