The functional group that can be identified through phthalein dye test is :

Step-by-step solution

The phthalein dye test is a characteristic test used for the identification of the phenolic functional group. When a phenol is heated with phthalic anhydride in the presence of concentrated sulfuric acid, it undergoes a condensation reaction to form a colorless compound, phenolphthalein. Upon adding an alkaline solution like dilute sodium hydroxide (NaOH) to this mixture, a characteristic pink or red color is produced due to the formation of the phenolphthalein anion. Therefore, the functional group identified thro