Question

A testtube contains solution of NaOH and Phenolphthalein. Why the colour

of the solution changes when HCl in added to it.​

Answer 1

because of neutralisation and the resultant solution becomes neutral. Therefore the color of solution changes from pink to colorless

Answer 2

Answer:

because phenolphthalein is weakly acidic in nature.and in aqueous solution it dissociates into and ions .the pink colourof the solution is due to concentration of ions in the solution