How does phenolphthalein appear in an acidic solution?

Correct answer: Colourless

Phenolphthalein is an acid-base indicator whose colour depends on the pH of the solution. In an acidic medium, its indicator form remains colourless; it becomes pink or magenta only in a sufficiently basic medium. Therefore, the absence of colour identifies the acidic condition in this test. The pink option belongs to the basic response, while blue and green are not the characteristic phenolphthalein colours. Option B is correct.