A student adds phenolphthalein to a colourless solution and observes a pink colour. Then dilute hydrochloric acid is added slowly and the pink colour disappears. Which conclusion is most correct?

Correct answer: The solution was basic and moved toward neutralisation after adding acid

Phenolphthalein is pink in a basic solution and colourless when the solution is acidic or sufficiently near neutral. The initial pink colour therefore shows that the sample was basic. Adding hydrochloric acid supplies H⁺ ions, which react with OH⁻ ions and reduce the basicity; as the mixture approaches neutralisation, the pink colour disappears. Hence option A is correct, while the other choices reverse indicator behaviour or misread the change.