Phenolphthalein is a pH indicator that is a reddish color at neutral but becomes bright yellow at acidic pH. Suppose you inoculate a tube of growth media containing phenolphthalein with a pure culture of an unknown microorganism, and after 24 hours the media starts to turn yellow. What can you conclude

The medium is acidic.

Explanation:

We can conclude that the media is acidic in nature because yellowing of the media and we know that yellowing of the media means acidic nature. If the colour of the media is reddish it means that the media has neutral pH. We know that Phenolphthalein is a pH indicator that tells us about the pH of the medium on which a microorganism grow. This chemical allow us to find out the acidity of the medium for the growth of microbes.