If blue litmus turns red and methyl orange turns red in a solution, which substance can neutralise it?

Correct answer: Sodium hydroxide solution

Both observations identify the test solution as acidic: blue litmus turns red in acid, and methyl orange is red in a sufficiently acidic medium. Neutralisation requires an acid to react with a base, forming salt and water. Sodium hydroxide solution is a base and supplies hydroxide ions that combine with hydrogen ions. Lemon juice, vinegar, and hydrochloric acid are acidic, so they would not appropriately neutralise this solution. Therefore option A is correct.