Methyl orange is red and phenolphthalein is colourless in a solution. What should be added to neutralise it?

Correct answer: Basic solution

Red methyl orange indicates an acidic medium, while colourless phenolphthalein is also consistent with an acidic solution. To neutralise an acid, a suitable base is added so that hydrogen ions react with hydroxide ions to form water: H⁺ + OH⁻ → H₂O. The quantity must be controlled to avoid making the mixture strongly basic. Therefore option A is correct; salt and sugar do not provide the required neutralisation.