Phenolphthalein is an acid base indicator. what color does it possess in the presence of excess hydrogen (i. e., hydronium) ions?

Colourless

Explanation:

Phenolphthalein is an acid-base indicator and is commonly employed in acid-base titration experiments.

Phenolphthalein is weakly acidic. Its ions are pink in colour whereas the molecule is colourless.

When phenolphthalein is in the presence of excess hydrogen ions i.e. in an acidic solution, its colour is colourless because it retains its molecular state (because it is itself an acid) but when it is in the presence of a basic solution it dissociates into ionic form to neutralize the excessive hydroxide ions of base and therefore the solution turns pink.

6.4 cm (max) - 25 cm (min)