If a substance gives hydroxide ions in water, what effect will its solution show on an indicator?

Correct answer: It will turn red litmus blue

The governing concept is the definition of a base in aqueous solution: it produces hydroxide ions or increases their concentration. Basic solutions turn red litmus paper blue. They generally turn phenolphthalein pink and methyl orange yellow, so the statements saying these indicators are always colourless or red are incorrect. Blue litmus is associated with acids turning it red, not with bases. Therefore option A is correct.