If phenolphthalein is pink and methyl orange is yellow, what is the nature of the solution?

Correct answer: Basic

The governing concept is the colour response of acid–base indicators. Phenolphthalein becomes pink in a basic medium, while methyl orange is yellow in a neutral or basic medium and red in an acidic medium. Since both observed colours are consistent with a basic solution, option A is correct. An acidic solution would make methyl orange red, and insolubility is not a measure of pH.