Phenolphthalein belongs to which of the following classes of dyes?

Step-by-step solution

Phenolphthalein is synthesized by the condensation of one molecule of phthalic anhydride with two molecules of phenol in the presence of a dehydrating agent such as concentrated sulfuric acid. Due to its structural origin from phthalic anhydride and phenol, it is classified under the category of phthalein dyes. Answer: Phthalein dyes