In the fountain experiment, what is the colour change observed when colourless phenolphthalein solution is added to a flask containing ammonia?

The correct option is A. Pink

Phenolphthalein is an indicator that turns colourless in acidic solution and pink or magenta in basic solutions. We know that ammonia is basic in nature. Therefore in the fountain experiment, the colourless phenolphthalein solution turns from colourless to pink when it is injected into a flask containing ammonia.