Phenolphthalein is colourless and methyl orange is red in a solution. What is the nature of this solution?

Correct answer: Acidic

Indicator colours reveal the approximate nature of a solution. Phenolphthalein is colourless in acidic and neutral media and turns pink in a sufficiently basic medium. Methyl orange is red in an acidic medium, yellow in a basic medium, and orange near its transition range. The simultaneous observations—colourless phenolphthalein and red methyl orange—therefore indicate an acidic solution. Option B is correct; a basic solution would make methyl orange yellow and usually phenolphthalein pink.