If a solution turns red litmus blue and phenolphthalein pink, what is the nature of the solution?

Correct answer: Basic

Indicators provide the governing evidence for classification. A basic solution changes red litmus to blue, and phenolphthalein is pink in a basic medium. Since both independent observations indicate the same nature, the solution is basic and option B is correct. An acidic solution would turn blue litmus red and keep phenolphthalein colourless; a neutral solution would not produce these changes. Saltiness alone does not determine pH.